Information

Scottish Health Survey 2012 - Volume 2 Technical Report

Technical report accompanying the release of the 2012 Scottish Health Survey

This document is part of a collection


Chapter 1: Methodology and Response

Joan Corbett, Michael Davidson, Shanna Dowling, Stephen Hinchliffe & Lisa Rutherford

1.1 Introduction

1.1.1 The Scottish Health Survey series

The Scottish Health Survey (SHeS) series was established by the Scottish Office in 1995 to provide data about the health of the population living in private households in Scotland.

The 1995 and 1998 surveys were carried out by the Joint Health Surveys Unit of the National Centre for Social Research and the Department of Epidemiology and Public Health, University College London Medical School (UCL). In 2003, a third organisation, the MRC Social and Public Health Sciences Unit at the University of Glasgow (MRC SPHSU) also joined the consortium.

As a result of a review by the then Scottish Executive[1] in 2005/06, the survey has been conducted annually since 2008. A consortium made up of ScotCen Social Research (a branch of NatCen Social Research), UCL and MRC SPHSU carried out the 2008-2011 surveys.

ScotCen Social Research and MRC SPHSU are carrying out the 2012-2015 surveys in collaboration with the Centre for Population Health Sciences, Edinburgh University and the Public Health Nutrition Research Group, Aberdeen University.

Each year, the survey consists of a set of core questions and measurements (for example, anthropometric and, if applicable, blood pressure measurements and analysis of urine and saliva samples), plus modules of questions on specific health conditions. As with the earlier surveys in the series, the principal focus of the 2012-2015 surveys is on cardiovascular disease (CVD) and related risk factors. CVD is one of the leading contributors to the global disease burden. Its main components are ischaemic heart disease (IHD) and stroke. IHD is the second most common cause of death in Scotland after cancer.[2] The SHeS series now has trend data going back 17 years; providing the time series is an important function of the survey.

1.1.2 Key changes to the survey methodology in 2012-2015

A number of changes to the survey methodology were proposed during a review by the Scottish Government of all the major household surveys in Scotland. These changes were adopted for SHeS in 2012-2015. The key methodological changes introduced in 2012 were:

Sample drawn by the Scottish Government
Prior to 2012, the contractor for SHeS drew the sample for each survey year. For the 2012-2015 surveys, the sample is being drawn by the Scottish Government in conjunction with the samples for two of the other large population surveys commissioned by the Scottish Government (the Scottish Household Survey and the Scottish Crime and Justice Survey). This approach reduces the burden on households in Scotland as they can only be selected once to take part in one of the three surveys in the 2012-2015 period (see Section 1.2 for further discussion of the sampling strategy).

Harmonised core questions
From 2012, there are around 20 core questions that will appear in all three of the Scottish Government population surveys each year. As a result it will be possible to conduct detailed analysis, by small geographical areas and subgroups for these key indicators. Further information about the harmonised core questions can be found here: http://www.scotland.gov.uk/Topics/Statistics/About/SurveyHarm

Reduced sample size
The sample size on SHeS has varied over the years. While in 2008-2011 the aim was to achieve 6,400 interviews with adults and 2,000 interviews with children each year, this has been reduced to a target of 4,000 adult and 1,800 child interviews annually for the 2012-2015 surveys.

Discontinuation of the Knowledge, Attitudes and Motivations to Health module
The NHS Health Scotland funded module of questions on knowledge, motivations and attitudes to health which was included in the 2008-2011 surveys was discontinued in 2012.

Interviewer administered biological samples and measurements
Since its inception in 1995, the SHeS interview included a second stage follow-up visit from a survey nurse to collect biological samples and measures. Prior to 2008 all participants were eligible to take part in this visit and between 2008 and 2011, a sub-sample of adult participants were invited to take part. The stage 2 nurse visit was discontinued in 2012. Instead, between 2012 and 2015, specially trained interviewers are taking many of the measurements and samples previously collected by survey nurses. As in 2008-2011, only a sub-sample of adult participants are eligible for the additional biological measures and samples. If the eligible participant agrees, they are offered the option of completing the module either at the end of the main interview or at another more convenient time.

Lung function, demispan and hip measurements are not included from 2012 onwards. In 2012 the biological module included:

  • blood pressure
  • questions on depression, anxiety and self-harm
  • waist measurement
  • saliva sample
  • urine sample

1.1.3 The 2012 survey

The 2012 SHeS was designed to provide data at national level about the population living in private households in Scotland. The eligible age range for the survey in 2012 was all aged 0+.

An initial sample of 9,555 addresses was drawn from the Postcode Address File (PAF). These addresses were comprised of three sample types: 4,459 formed the main (core) sample, at which up to ten adults and up to two children per household were eligible to be interviewed; 4,140 addresses formed an additional child boost sample, at which only households containing children aged 0-15 were eligible to participate (up to two children at these households were eligible to be interviewed); the remaining 956 addresses formed the Health Board boost sample at which only adults were eligible for interview. Fife, Grampian and Dumfries & Galloway NHS Health Boards opted to boost the number of adults (16+) interviewed in their area in 2012. Children were not eligible to participate at Health Board boost addresses.

The 9,555 addresses were grouped into 417 interviewer assignments, with around 35 assignments being issued each month to interviewers between January 2012 and December 2012.

Sample type Number of addresses issued in 2012
Main 4,459
Child Boost 4,140
Health Board Boost 956
Total 9,555

Data collection involved a main (core) interview, and if applicable, adults also completed the biological module. Of the 4,459 main addresses issued, 1,466 were flagged as eligible for the 'biological module sample'. At these addresses all adults (16+) that participated in the main interview were eligible to take part in the module. Only interviewers that were specially trained in administering biological measures and samples were allocated these addresses to work on. There was no biological module at the remaining main (core) sample addresses or at child boost or health board boost addresses.

1.1.4 The 2012 reports

The 2012 SHeS report consists of two volumes, published as a set as 'The Scottish Health Survey 2012.' Volume 1 presents results for adults and children on a variety of health topics. Volume 2 provides methodological information and survey documentation. Both volumes are available on the Scottish Government's SHeS website along with a short summary report of the key findings from Volume 1 (www.scotland.gov.uk/scottishhealthsurvey). From 2012 onward, paper versions of the report are no longer available.

1.1.5 Comparisons with previous surveys in the SHeS series

In the 2012 report comparisons are made with data collected earlier in the series (1995-2011). Having such an extensive trend period makes it possible to comment on whether any changes in health behaviours identified between years were real or an instance of sample fluctuation.

1.1.6 Health Board level analysis

Since 2008, the SHeS sample has been designed to be representative at the Health Board level (for all boards) after four years of data collection have taken place. Analysis of the 2008 to 2011 data by NHS Health Board was published in 2012 and is available on the SHeS website (www.scotland.gov.uk/scottishhealthsurvey). For this reason, the 2012 report does not include any analysis by NHS Board and the next Board level analysis is not due to be published until 2016 (results aggregated for years 2012-2015). Health Boards with larger samples may be able to analyse their own data before this time and users should consult the SHeS website for further guidance on analysis at different sub-geographies.

1.1.7 Access to data

The 2012 SHeS data will be deposited at the UK Data Archive at the University of Essex, from where earlier years' datasets and combined years datasets can also be obtained (www.data-archive.ac.uk).

1.2 Sample Design

1.2.1 Requirements

The sample for the 2012-2015 Scottish Health Surveys was designed by the Scottish Government. The sample design was coordinated with the sample designs for the Scottish Household Survey and the Scottish Crime and Justice Survey as part of a survey efficiency project and to allow the samples of the three surveys to be pooled for further analysis.[3]

There were three elements to the SHeS sample:

1 Main adult sample to allow annual reporting of Scotland level results and results for Health Boards at the end of the 2012-2015 four year cycle. This required an annual interview target of 4,000 adults for Scotland as a whole and a minimum of 125 adults for each Health Board. In addition, within the main sample there was a requirement for 1,000 adults to complete a biological module each year.

2 Child sample boost - overall there was a requirement for 1,780 child interviews for Scotland. The main sample was only expected to yield 780 child interviews so a further 1,000 interviews were required from a boost sample.

3 Health Board boosts - in 2012 Dumfries and Galloway, Grampian and Fife Health Boards opted to boost the number of adults interviewed in their Health Board. Each Health Board specified the target number of interviews for their boosts.

1.2.2 Sample design and assumptions

For all three elements, the 2012 Scottish Health Survey used a two-stage clustered sample design with intermediate geographies[4] randomly selected at the first stage and address points at the second stage. With the exception of Orkney, Shetland and Western Isles (where datazones were used for clustering), the sample was clustered by intermediate geographies (IG) with one quarter of IGs selected for each year of fieldwork. This means that over four years of fieldwork all IGs are included in the sample and that the combined 2012-2015 sample is unclustered.

1.2.3 Main sample

As stated above, the annual sample size for Scotland in 2012 was 4,000 adults with a minimum of 125 adults in each Health Board. These were the minimum sample sizes required to allow effective reporting of Scotland-level results each year and Health Board results at the end of the four year (2012-2015) cycle. An iterative approach was taken to efficiently allocate the sample across all Health Boards. For the first iteration 4,000 adult interviews were allocated across Health Boards in proportion to the adult population. Any Health Boards allocated fewer than 125 adult interviews had their allocation increased to 125.

The remaining sample was then allocated over the remaining Health Boards. Where allocations were not whole numbers the number was rounded up. This resulted in a total target of 4,006 adult interviews. The results of the allocation are shown in Figure 1A.

Figure 1A: SHeS target annual adult interviews, 2012-2015, by Health Board

Health Board Target Annual Adult Interviews
Ayrshire and Arran 256
Borders 125
Dumfries and Galloway 125
Fife 252
Forth Valley 201
Grampian 379
Greater Glasgow and Clyde 836
Highland 217
Lanarkshire 383
Lothian 578
Orkney 125
Shetland 125
Tayside 279
Western Isles 125
Total 4,006

While the required sample sizes were set at Health Board (HB) level, to allow for coordination with the sample selection of the SHS and SCJS, the sample design was implemented using local authorities (LA) as strata. This was done by allocating the target Health Board samples to local authorities proportionate to population.

There was a slight complication in the design due to local authority boundaries not being concurrent with Health Board boundaries. Where there was less than 2% of the local authority population outwith its main Health Board, it was assumed that the local authority was entirely located within the Health Board. This gave the following assumptions:

  • Dumfries and Galloway LA lies completely in Dumfries and Galloway HB
  • Perth and Kinross LA lies completely in Tayside HB
  • Scottish Borders LA lies completely in Borders HB
  • Falkirk LA lies completely in Forth Valley HB
  • East Renfrewshire LA lies completely in Greater Glasgow and Clyde HB
  • Glasgow City LA lies completely in the Greater Glasgow and Clyde HB
  • Stirling LA lies completely in Forth Valley HB
  • West Lothian LA lies completely Lothian HB

For North Lanarkshire and South Lanarkshire, 5.6% and 22.3% of the respective populations are located in Greater Glasgow and Clyde Health Board rather than Lanarkshire Health Board. Therefore, the sample stratification for the North Lanarkshire and South Lanarkshire local authority areas were each split into two with the west elements lying in Greater Glasgow and Clyde and the east elements lying in Lanarkshire.

The number of addresses selected in order to provide the target number of interviews was calculated by:

1. Estimating the number of productive adult interviews per co-operating household. Based on response data to the 2008 and 2009 surveys, it was estimated that there would be 1.5 interviews per co-operating household in Greater Glasgow and Clyde and 1.55 interviews in all other Health Boards.

2. Allocation of the target interviews and associated estimate of co-operating households to local authority strata proportionate to population.

3. Response rate assumptions were required in order to estimate the number of eligible addresses needed to yield the cooperating households target for each stratum. The response rate assumptions were applied according to the groups of local authorities shown in Figure 1B. The groupings were used as there was insufficient historic information on which to base individual local authority assumptions. Furthermore, Health Boards could not be used as there was a high degree of variability of response rates for local authorities within the same Health Boards. Therefore, local authorities were placed in 9 groups which had common attributes and comparable response rates. The response rate assumptions for the local authority groups were based on the weighted average for 2009.

4. The final step was to estimate the level of ineligible addresses. The estimates were calculated at local authority level and based on the average level of ineligible addresses from the Scottish Health Survey, Scottish Household Survey, Scottish Crime and Justice Survey, and Scottish House Condition Survey from 2007 to 2009/10.

Figure 1B: Local authority groupings for response rate assumptions

Local authority group Constituent local authorities
Ayrshire & Arran and Dumfries & Galloway East Ayrshire, North Ayrshire, South Ayrshire, Dumfries and Galloway
Highlands Aberdeenshire, Argyll and Bute, Highland, Moray
Islands Western Isles, Orkney Islands, Shetland Islands
West East Renfrewshire, East Dunbartonshire, West Dunbartonshire, Renfrewshire, Inverclyde
Large Cities Aberdeen City, City of Edinburgh, Glasgow City
Lothian and Borders West Lothian, East Lothian, Midlothian, Scottish Borders
Tayside Perth and Kinross, Angus, Dundee City
Forth Valley and Fife Clackmannanshire, Fife, Stirling, Falkirk
Lanarkshire North Lanarkshire, South Lanarkshire

Figure 1E shows the number of selected addresses for the main sample in 2012.

1.2.4 Child boost sample

A total of 1,780 child interviews were required each year for the 2012-2015 surveys. Based on the 2009 survey, it was estimated that the main sample would provide 780 child interviews, therefore, to reach the target number of child interviews, a child boost sample was required to yield a further 1,000 interviews.

While the target number of interviews was specified at Health Board level, as with the main sample, the child boost sample was stratified by local authority. The process for calculating the number of addresses to select was as follows:

1. The overall target sample of 1,780 child interviews was allocated proportionally to Health Boards based on the child (those aged under 16) population. The expected number of child interviews from the main sample was then subtracted from the overall target sample to obtain the child boost target sample for Health Boards. If the number expected from the main sample was greater than the overall required number of child interviews for a Health Board then the boost target was set to zero and the remaining sample was redistributed so the overall target remained at 1,780. The following table shows the target sample sizes for the main sample and child boost sample by Health Board.

Figure 1C: SHeS target annual child interviews, 2012-2015, by HB

Health Board Expected child interviews from main sample Child interviews from boost Total child interviews
Ayrshire and Arran 50 73 123
Borders 24 14 38
Dumfries and Galloway 24 24 48
Fife 49 75 124
Forth Valley 39 64 103
Grampian 73 108 181
Greater Glasgow and Clyde 167 229 396
Highland 42 60 102
Lanarkshire 74 127 201
Lothian 112 155 267
Orkney 24 0 24
Shetland 24 0 24
Tayside 54 76 130
Western Isles 24 0 24
Total 780 1005 1785

2. Performance in the 2008 and 2009 child boost samples were used to estimate the required number of co-operating households with children in each Health Board.

3. To estimate the proportion of childless households, data from the 2007 and 2008 Scottish Household Surveys was used. As there was little variation across different areas a Scotland level estimate of households without children (74.6%) was used.

4. Analysis of survey response to the child boost samples in the 2008 and 2009 surveys found that the response rate was consistently higher for the child boost than the main sample. Therefore, the estimated response rates for the child boost sample were set at 6% higher than the main sample response rate for each local authority area.

5. The ineligible address assumptions for the main sample were applied to the sample address calculations for the child boost sample.

The total number of addresses selected for the child boost sample are shown in Figure 1E.

1.2.5 Health Board boost samples

Individual Health Boards were given the opportunity to fund a boost to their sample to allow them to get local level results more frequently or to allow analysis below Health Board level after four years. For 2012, Dumfries and Galloway, Fife and Grampian opted to boost their adult samples. The following table shows the target sample size for each of the three Health Boards.

Figure 1D: Target sample for Health Board boosts

Health Board Target interviews for boost
Dumfries and Galloway 300
Fife 300
Grampian 300
Total 900

The main sample was selected before the areas opting to boost were confirmed so boost samples were supplementary to the main sample. For Dumfries and Galloway and Grampian the sample design followed the process outlined above for the main sample. Fife Health Board requested that the combined main sample and boost sample was equally distributed across its three Community Health Partnership areas. This required an extra level of stratification for Fife before the process above could be followed. The same active PSUs as the main sample were used for the Health Board boost samples.

Figure 1E: Selected addresses by strata

Sample strata Main sample selected addresses Health Board boost samples Child boost sample selected addresses Total sampled
Aberdeen City 188 149 173 510
Aberdeenshire 170 135 201 506
Angus 81 - 86 167
Argyll & Bute 73 - 70 143
Clackmannanshire 36 - 44 80
Dumfries & Galloway 128 306 92 526
Dundee City 109 - 107 216
East Ayrshire 83 - 90 173
East Dunbartonshire 85 - 87 172
East Lothian 70 - 82 152
East Renfrewshire 72 - 83 155
Edinburgh, City of 431 - 365 796
Eilean Siar 131 - 0 131
Falkirk 109 - 129 238
Fife 264 315 293 872
Glasgow City 538 - 492 1030
Highland 166 - 178 344
Inverclyde 70 - 69 139
Midlothian 57 - 66 123
Moray 64 51 70 185
North Ayrshire 95 - 106 201
North Lanarkshire East 219 - 278 497
North Lanarkshire West 15 - 17 32
Orkney Islands 124 - 0 124
Perth & Kinross 112 - 114 226
Renfrewshire 144 - 146 290
Scottish Borders 138 - 58 196
Shetland Islands 121 - 0 121
South Ayrshire 79 - 78 157
South Lanarkshire East 183 - 218 401
South Lanarkshire West 44 - 45 89
Stirling 65 - 76 141
West Dunbartonshire 76 - 78 154
West Lothian 119 - 149 268
Total 4,459 956 4,140 9,555

1.2.6 Sample Selection

The Royal Mail's small user Postcode Address File (PAF) was used as the sample frame for the address selection. The advantages of using the PAF are as follows:

  • It has previously been used as the sample frame for Scottish Government surveys so previously recorded levels of ineligible addresses could be used to inform assumptions for 2012 sample design
  • It has excellent coverage of addresses in Scotland
  • The small user version excludes the majority of businesses

The Assessor's Portal which is the council tax list of all dwellings in Scotland was considered as an alternative sample frame but since it had not previously been used as a sample frame for large scale surveys in Scotland there would have been a greater risk attached to assumptions for response rates and ineligible addresses.

The PAF does still include a number of ineligible addresses, such as small businesses, second homes, holiday rental accommodation and vacant properties. A review of the previous performance of individual surveys found that they each recorded fairly consistent levels of ineligible address for each local authority. This meant that robust assumptions could be made for the expected levels of ineligible addresses in the sample size calculations.

As the samples for the SHeS, SHS and SCJS are all being drawn by the Scottish Government from 2012 onwards, addresses selected for any of the surveys are removed from the sample frame so that they cannot be re-sampled for another survey. This will help to reduce respondent burden. The addresses are removed from the sample frame for a minimum of 4 years.

The sample design specified Section 1.2.1 was implemented in three stages:

1. All primary sampling units (which were datazones on the islands and intermediate geographies elsewhere) were randomly allocated to one of the four years of fieldwork. This meant that each year the sample was drawn from one quarter of PSUs and ensured that over four years (2012-2015) of fieldwork all addresses had a non-zero probability of selection. One quarter of the target adult sample was also required to complete the biological module. To make fieldwork more efficient, rather than randomly allocating addresses from the entire survey to the module, each year primary sampling units were allocated to the biological module with all selected addresses within those PSUs being eligible for the biological interview. While one-quarter of the sample was required to complete the biological module, to guard against a lower response rate, in 2012, 32% of PSUs were allocated to the biological module.

Figure 1F: Primary sampling units selected, 2012

Health Board PSUs in 2012 Sample Total PSUs
Angus 23 90
Ayrshire and Arran 23 92
Borders 7 29
Dumfries and Galloway 8 35
Fife 26 103
Forth Valley 18 74
Grampian 32 128
Greater Glasgow and Clyde 68 273
Highland 19 76
Lanarkshire 34 137
Lothian 45 177
Orkney 6 27
Shetland 7 30
Western Isles 9 36
Total 325 1,307

2. The required number of addresses for the main sample and child boost sample were combined to give an overall total number of addresses to sample for each stratum. The overall number of addresses for each stratum was then sampled from the sampling frame of addresses in active PSUs. Systematic random sampling was used with addresses within PSUs ordered by urban-rural classification, SIMD rank and postcode.

3. Once the overall sample was selected each address was randomly allocated to the main sample or the child boost sample.

1.2.7 Selecting households at addresses with multiple dwellings

A small number of addresses have only one entry in the PAF but contain multiple dwelling units. Such addresses are identified in the PAF by the Multiple Occupancy Indicator (MOI). To ensure that households within MOI addresses had the same probability of selection as other households, the likelihood of selecting the addresses was increased in proportion to the MOI. At addresses with more than one dwelling unit fieldworkers have a programme to randomly select the household at which interviews should be sought. There are generally a few cases where the MOI on the PAF is inconsistent with the actual number of dwelling units. When this occurred, the fieldworkers recorded the information and a correction was made through the survey weighting.

1.2.8 Selecting individuals within households

For the main sample and the Health Board boost all adults aged 16 and over in responding households were selected for interview. To ease respondent burden, a maximum of two children were interviewed at each household for both the main sample and the child boost sample. If a household contained more than two children then two of them were randomly selected for interview.

1.3 Topic coverage

1.3.1 Introduction

The most recent consultation on the SHeS questionnaire was carried out in 2011, ahead of the 2012 to 2015 surveys. Many of the topics included in previous years of the survey have been included again in 2012 to 2015. As with previous years, the survey had a focus on cardio-vascular disease (CVD) and associated risk factors.

1.3.2 Documentation

Copies of all the survey data collection documents are included in Appendix A. Full copies of the main interview and biological module questionnaire documentation are also included in Appendix A. Protocols for measurements (height, weight, waist and blood pressure) and for the collection of biological samples (saliva and urine) are included in Appendix B. A summary of the content of the 2012 main interview and biological module is provided below.

1.3.3 Main interview

Information was collected at both the household and individual level. The table that follows summarises the content of the individual level interviews for all participants. The topics a participant was asked depended on both their age and the sample type they were allocated to. The age criteria for each topic is included in brackets after the topic name.

Version A households accounted for approximately two thirds of the core sample. At these households the questionnaire included the core questions and the Version A rotating module questions. Version B households accounted for the remaining third of the core sample. At these addresses participants were only asked the core questions and in addition, adult participants were also asked to take part in the biological module.

Core Version A topics in 2012 were: core interview topics plus respiratory symptoms, asthma, barriers and motivations to exercise, and adult eating habits.

Figure 1G: Content of the 2012 Interview

CORE SAMPLE - Main interview outline
Version A Version B
Household questionnaire including household composition
General health (0+) including caring (4+)
General CVD (16+)
Use of health services (0+)
Respiratory (16+) -
Asthma (0+)
Asthma (additional questions) (0+)
Physical activity adults (16+) and children (2-15)
Sedentary activity adults (16+) and children (2-15)
Barriers and motivations to exercise (16+)
Eating habits (16+)
Eating habits children (2-15)
Fruit and veg consumption (2+)
Vitamins and supplements (16+)
Smoking and Drinking (16+) [16-19 in a self completion]
Dental health (16+)
Economic activity (16+)
Education (16+) -
Ethnic background, religion and country of birth(0+)
Family health background and parental job details (16+)
Self-completions (13+ & parents of 4-12 yr olds)
Height (2+) and Weight (2+)
Data linkage and follow-up research consents (0+)
- Biological module (16+)

A number of changes were made to the questionnaire content in advance of the 2012 to 2015 surveys. All new, and amended questions, have been flagged in the full questionnaire documentation in Appendix A. In summary, the main changes to the questionnaire in 2012 were as follows:

General health and illness

The wording of the question about long-term conditions was amended slightly in 2012-2015 to bring it into line with the harmonised question used across all three of the Scottish Government large-scale household population surveys. Additional categories were also included for the question which asks about the extent to which a condition limits the participant's activities (yes, a little and yes, a lot).

Caring Responsibilities

  • The wording of the question about caring responsibilities was amended in 2012-2015 to bring it in line with the question used in the 2011 Census.
  • Questions on caring responsibilities were extended to children aged 4 to 15 (for children aged 4 to 12 parents would answer on their child's behalf).
  • Question on who care is being provided for were expanded to enable separate identification of outwith the household answer options.
  • The answer categories for the question on hours spent providing care were amended and aligned with the 2011 Census question.
  • Additional questions on hours spent providing care, impact of caring on employment and support for carers have been included.

CVD Conditions, High Blood Pressure and Diabetes
Questions on surgery and other treatment for conditions are no longer being asked in 2012-2015.

Self-reported Blood Pressure and Cholesterol Measurements
These questions have not been included in the 2012-2015 surveys.

Rose Angina
These questions have not been included in the 2012-2015 surveys.

Edinburgh Claudication
These questions have not been included in the 2012-2015 surveys.

Asthma
A reduced set of questions have been retained in the Version A module for 2012 and 2014. These include:

  • Prevalence of wheezing and whistling, details about attacks and whether wheezing or whistling has affected sleep or daily activities.
  • Three questions on wheezing and whistling were also been retained and moved to the core interview for 2012-2015. These questions are about prevalence of asthma.
  • Questions about breathlessness and treatment for asthma and wheezing or whistling are no longer being asked in 2012-2015.

MRC Respiratory Module
A reduced set of questions about phlegm and shortness of breath have been retained in the Version A module and will be included in the 2012 and 2014 surveys.

  • Questions about attacks of wheezing or whistling and shortness of breaths have not been included in the 2012-2015 surveys.

Adult Physical Activity
Additional questions on, muscle strengthening activities in adults aged 16 and over, balance improving activities in adults aged 65 and over and walking exertion in adults aged 65 and over have been included in 2012-2015. Questions on muscle strengthening and balance applied to sporting activities only.

  • An additional question which asks about participation in an extended range of sports has been added in 2012-2015.
  • The questions about physical activity at work which were previously asked of the household reference person in Core - Version A are not being asked in the 2012-2015 surveys.
  • A new question about length of time spent sitting down at work has also been included in 2012-2015.

Time spent in front of a screen (adults and children)

  • Questions about the amount of time spent sitting watching TV or in front of another type of screen have been retained and moved from the Version A module to the core interview. An additional question about time spent doing other sedentary activity during leisure time has been included in the 2012-2015 surveys.

Motivations and barriers to sport
Additional questions about motivations and barriers to sport have been added for adults in Version A in 2012 (and 2014).

Eating Habits and DINE questionnaire (Dietary Instrument of Nutrition Education)
Questions about eating poultry, drinking water and adding salt to dishes are not being included in the 2012-2015 surveys.

Vitamins and supplements

  • Questions about vitamin, mineral and supplement intake have been retained and moved to the core interview in the 2012-2015 surveys (previously this was asked during the nurse visit).
  • A previous question about type of vitamins, minerals or supplements consumed is not included in the 2012 to 2015 surveys.

Smoking behaviour
A new question on the length of time people, who had previously smoked, has been stopped for is included in the 2012-2015 surveys.

Nicotine replacement

  • Questions about nicotine replacement products and therapies have been moved to the core interview (in previous years these were included in the nurse interview).
  • Additional response categories have been added to the question asking which nicotine replacement products have been used.

Passive smoking

  • The question about passive smoking has been retained in 2012-2015 although the response categories have been adjusted to reflect the changes in legislation. The age range has also been extended and this question is now asked of all participants (children aged 0-15 were previously not asked this question).
  • A new question on smoking rules in the home has been included in the household questionnaire for the 2012-2015 surveys.

Alcohol consumption

  • The question about comparisons with drinking behaviour five years ago is no longer being asked in 2012-2015.
  • The questions about who people are with and where they consume the most alcohol have been retained but the secondary questions are no longer being asked in 2012-2015.
  • In 2012-2015, the self-completion CAGE problem drinking questionnaire has been replaced with the AUDIT questionnaire.

Parental health
New questions about family members' experience of heart disease, stroke and diabetes are being included in the core questionnaire on the 2012-2015 surveys.

National Identity
The question on a participant's national identity is not being asked in the 2012-2015 surveys.

Food poisoning
Questions about food poisoning are no longer being asked in 2012-2015.

Harmonised questions
In 2012, the Scottish Government introduced a set of core harmonised questions to their large cross-sectional population surveys. The purpose was to enable the data for these questions to be pooled across the surveys, providing better estimates for both smaller geographical areas and sub-groups at the national level.

This led to some changes to these questions on SHeS including minor changes to the wording on questions on car ownership, marital status, caring status and household income. There was also a change in the employment status questions to enable the International Labour Organisation's (ILO) definition of economic activity to be derived from the data. Questions with amendments made in 2012 are highlighted in the questionnaire documentation (Appendix A).

Questions about perceptions of crime were included in the survey for the first time in 2012. These are included in the household questionnaire and are only asked of one adult (the person answering the household questionnaire). The order that this set of questions is asked in has been randomised to minimise order effects.

An additional question about country of birth has also been added to the individual questionnaire and is asked of all respondents.

1.3.4 Self-completion questionnaire

Participants aged 13 and over were asked to fill in a self-completion booklet during the interview. In all, four different booklets were used in the survey. The version administered was dependent on a participant's age.

The booklet for young adults aged 16-17 asked about smoking and drinking behaviour (instead of the CAPI interview). Interviewers also had the option of using this young adults booklet for those aged 18-19 if they felt that it would be more appropriate for them to answer the questions in this format rather can face to face (e.g. might be more likely to give more honest answers than in the face to face interview when other household members may be present).

Booklet for adults AUDIT

questionnaire (designed to identify signs of hazardous or harmful drinking or possible alcohol dependence),GHQ12, Warwick Edinburgh Mental Well-being scale (WEMWBS), gambling, use of contraception, and sexual orientation

Booklet for young adults

Smoking, drinking, AUDIT questionnaire (designed to identify signs of hazardous or harmful drinking or possible alcohol dependence), GHQ12, WEMWBS, gambling, use of contraception, and sexual orientation

Booklet for 13-15 year olds

GHQ12 and WEMWBS

Booklet for parents of 4-12

Strengths and Difficulties Questionnaire year olds (SDQ) designed to detect behavioural, emotional and relationship difficulties in children.

1.3.5 Height and Weight

Interviewers measured the height and weight of all participants aged 2 and over. Protocols for taking height and weight measures are included in Appendix B.

1.3.6 Biological module

As highlighted previously, the nurse visit was discontinued after the 2011 survey. From 2012 to 2015, specially trained interviewers are instead collecting some of the measurements and samples previously collected by nurses.

At a sub-sample (of around a third) of main sample addresses, adults (aged 16 and over) were eligible to complete the biological module. The module could either be completed immediately after the main interview or on a separate occasion.

Participants were asked whether they used any medicines, pills, syrups, ointments, puffers or injections prescribed to them by a doctor or nurse. If participants answered yes to questions in the main interview about taking medication for high blood pressure, a heart condition or stroke then they would be asked to give the names of the drugs to the interviewer. This information is used to interpret blood pressure readings.

In addition to height and weight measurements, interviewers also took the following measurements from participants to the biological module: blood pressure and waist circumference. Written agreement was also sought to take samples of saliva (for the analysis of cotinine, a derivative of nicotine) and spot urine samples (for the analysis of dietary sodium). Lung function and hip measurements as well as blood samples taken by venepuncture were not included in 2012. The possibility of including dried blood spots, which would enable the analysis of total cholesterol, glycated haemoglobin and C-reactive protein, is currently being explored.

The set of questions about depression, anxiety, suicide attempts and self-harm (taken from the Adult Psychiatric Morbidity Survey) has been included in the survey since 2008.[5] Between 2008 and 2011 these questions were included in the nurse interview. In 2012, they were moved into the biological module and are now administered via computer assisted self-interviewing (CASI) instead of face to face CAPI. Three of the questions on self-harm previously included are not being asked in the 2012-2015 surveys.

Figure 1H: Content of the 2012 Biological Module

Outline of the Biological Module
Prescribed medicines (age 16+ if has heart condition, high blood pressure or has had stroke)
Blood pressure (age 16+)
Waist measurement (age 16+)
Use of Nicotine Replacement therapy (16+)
Saliva sample (age 16+)
Urine sample (age 16+)
Depression, anxiety, suicidal attempts and self-harm (age 16+)

1.4 fieldwork procedures

1.4.1 Advance letters

Each sampled address was sent an advance letter that introduced the survey and stated that an interviewer would be calling to seek permission to interview. Three versions of the advance letter were used in 2012; one for the core version A and Health Board boost addresses in the sample, one for the core version B (with the biological module) addresses and a separate version for the child boost addresses. A copy of the survey leaflet was included with every advance letter. The survey leaflet introduced the survey, described its purpose in more detail and included some summary findings from previous surveys.

1.4.2 Making contact

At initial contact, the interviewer established the number of dwelling units (DUs) and/or households (HHs) at an address and made any necessary selections (see Section 1.2).

The interviewer then attempted to make contact with each household. In the main sample they attempted to interview all adults (up to a maximum of ten) and up to two children aged 0-15 (see Section 1.2). At child boost sample households, interviewers first screened for children aged 0-15. In those households where children were present up to two children were selected for interview. Interviewers sought the consent of the parent and the child before the interview. At Health Board boost sample households interviewers attempted to interview a maximum of ten adults at selected households.

1.4.3 Collecting data

Interviewers used computer assisted interviewing.

At each co-operating eligible household in all sample types, the interviewer first completed a household questionnaire, information being obtained from the household reference person[6] or their partner wherever possible. This questionnaire obtained information about all members of the household, regardless of age. The CAPI program then created individual questionnaires for each eligible participant in the household.

An individual interview was carried out with all selected adults and children in a household. In order to reduce the amount of time spent in the home, interviews could be carried out concurrently, with the program allowing up to four participants to be interviewed concurrently in a session.

Height and weight measurements were obtained towards the end of the interview.

In addition to an advance letter and general survey leaflet, participants were also given a more detailed leaflet describing the contents and purpose of the interview. Adults in households eligible for the biological module were given a longer version of this leaflet, (as well as a Measurement Record Card) providing information on each of the measurements and samples being taken. A separate version of this leaflet was used for children in the main and child boost households. Parents at child boost addresses were also given a leaflet containing background information on the survey. Participant leaflets are included in Appendix A.

1.4.4 Introducing the biological module

Only a sub-sample of adults in the main sample was eligible to take part in the biological module. At the end of the main interview, adult participants at the Version B addresses were asked for their agreement to take part in the biological module stage of the survey. Wherever possible, interviewers would carry out the measurements and collect the samples directly after the main interview. If this was not possible the interviewer would arrange to go back at a convenient time to complete this part of the survey. During this module the interviewer carried out the measurements described in Section 1.3.6 and obtained the saliva and urine samples from those adults eligible and willing to provide these samples. Written consent was obtained from participants before saliva and urine samples were taken.

1.4.5 Interviewing and measuring children

Children aged 13-15 were interviewed directly by interviewers, permission having first been obtained from the child's parent or guardian. Interviewers were instructed to ensure that the child's parent or guardian was present in the home throughout the interview. Information about younger children was collected directly from a parent/guardian. Whenever possible, younger children were present while their parent/guardian answered questions about their health. This was partly because the interviewer had to measure their height and weight and it also ensured that the child could contribute information where appropriate.

1.4.6 Feedback to participants

If participants wished, interviewers recorded height and weight measurements on their information leaflet.

Participants eligible for the biological module were also given a Measurement Record Card which had more information on the measurements and sample that the interviewers administered. If participants had their waist measurement and blood pressure taken then interviewers recorded their results on this card (if the participant wished). Prior to 2012 blood pressure results were sent to a participant's GP along with blood sample results if the respondent wished but this is no longer the case.

Interviewers were issued with a set of guidelines to follow when commenting on participants' blood pressure readings (see Appendix B for details). If an adult's blood pressure reading was severely raised, interviewers were instructed to contact the Survey Doctor at the earliest opportunity. The Survey Doctor would then phone the participant and advise them to contact their GP as soon as possible.

1.5 Fieldwork quality control and ethical clearance

1.5.1 Training interviewers

Interviewers were fully briefed on the administration of the survey, including screening for households with children in the child boost sample. They were also trained and accredited in measuring height and weight.

Interviewers interested in administering the biological module were initially screened for suitability. Minimum competency levels and experience in relation to SHeS were set and only interviewers that met the criteria were invited to the training and accreditation sessions.

Training to administer the biological module took place over three days. At the end of the training session interviewers were accredited on administering each of the measurements and samples and were only able to work on the module if they passed their accreditation.

Interviewers were also accompanied by a nurse supervisor (with previous experience of working on the survey) on their first visit. They are also supervised in the field every six months by an experienced survey nurse to ensure they are administering the measurements and samples in line with SHeS protocols.

Full sets of written instructions, covering both survey procedures and measurement protocols, were provided for interviewers (Appendix B contains a copy of the measurement protocols).

Interviewers who had not previously worked on SHeS were accompanied by an interviewer supervisor during the early stages of their work to ensure that interviews and protocols were being correctly administered.

1.5.2 Checking interviewer and measurement quality

A large number of quality control measures were built into the survey at both data collection and subsequent stages to check on the quality of interviewer performance.

Recalls to check on the work of interviewers were carried out at 10% of productive households.

The computer program used by interviewers had in-built soft checks (which can be suppressed) and hard checks (which cannot be suppressed) which included messages querying uncommon or unlikely answers as well as answers outside an acceptable range. For example, if someone aged 16 or over had a height entered in excess of 1.93 metres, a message asked the interviewer to confirm that this was a correct entry (a soft check), and if someone said they had carried out an activity on more than 28 days in the last four weeks the interviewer would not be able to enter this (a hard check). For children, the checks were age specific. Some infants were weighed by having an adult hold them; the weight of the adult on their own was entered into the computer followed by the combined weight of the infant and adult. A hard check was used to ensure that the weight entered for the adult alone did not exceed the weight of the infant and adult combined.

1.5.3 Ethical clearance

Ethical approval for the 2012 survey was obtained from the Multi-Centre Research Ethics Committee for Wales (REC reference number: 11/WA/0246).

1.6 Survey Response

1.6.1 Introduction

This section presents the fieldwork outcomes for the sampled addresses in 2012. Survey response is an important indicator of survey quality as non-response can introduce bias into survey estimates. Standardised outcome codes (based on an updated version of those published in Lynn et al (2001)[7] for survey fieldwork were applied across the SHeS, SHS and SCJS to allow for consistent reporting of fieldwork performance and effective comparison of performance on the surveys.

1.6.2 Household response

Table 1.1 shows a detailed breakdown of the SHeS response for all sampled addresses for Scotland using the standardised outcome codes cited above. The addresses of unknown eligibility have been allocated as either eligible or ineligible proportional to the levels of eligibility for the remainder of the sample. This approach provides a conservative estimate of the household response rate as it estimates a high proportion of eligible cases among those addresses with unknown eligibility.

In each selected household in the main sample all adults and a maximum of two children were eligible for interview. When considering the household response rate, households classed as "responding" were those where at least one eligible person was interviewed. The table shows that for the combined main and boost sample 65.8% of eligible households were classed as responding with all individual interviews complete at 51.1% of households.

For the child boost sample 71.9 of selected addresses were ineligible as the households did not contain any children under the age of 16. For eligible households 70.5% were classed as responding, with almost all possible interviews being completed in the responding households.

Table 1.2 shows that across Heath Boards the household response rate for the main (including Health Board boost sample) ranged from 58% (Lanarkshire) to 80% (Western Isles). Fully cooperating households were those where all eligible individuals were interviewed, had height and weight measured and (if selected) completed the biological module.

Table 1.3 shows that the household response rate for eligible addresses in the child boost sample varied between 60% (Highland) and 94% (Dumfries and Galloway). Table 1.1 - Table 1.3

1.6.3 Individual response for adults

Overall, in 2012, there were 4,815 interviews with adults with 1,020 also taking part in the biological module.

In order to calculate the adult response rate, since all adults in households were eligible for interview, the number of adults in non-responding households had to be estimated to calculate the total number of adults in all eligible households. This was done by calculating the average number of adults per household for responding households and non-responding households (where information on the composition is known) and then applying this to the households where nothing was known. The total estimated number of adults from sampled addresses eligible for interview is referred to as the "set" sample. For 2012 the set sample was 4,104 men and 4,546 women.

Table 1.4 shows the adult response rate broken down by gender. In 2012, the adult response rate was 52% for men, 59% for women and 56% overall.

In responding households (those households where at least one interview with an eligible person was completed) information on the age and gender of all members of the household (not just responding individuals) was collected. This allowed the consideration of response to stages of the survey by individual characteristics as shown in tables 1.5 and 1.6. Younger men and women had lower response rates (54% for men and 66% for women aged 16-24) than older age groups (over 90% response rate for men and women aged over 65).

As part of the biological module, respondents were asked to have their waist and blood pressure measured and to provide saliva and urine samples. Almost all individuals completing the biological module interview allowed the waist and blood pressure measurements to be taken but there was a drop off in providing the samples. Of those eligible for the biological module, a urine sample was either refused or not obtained for 9% of men and 14% of women.

Table 1.9 shows that men are under-represented in the SHeS sample compared to NRS population estimates as they made up 44% of the sample but 48% of the population. Younger age groups were also under-represented in the SHeS sample when compared to NRS population estimates. In particular, men under 35 and women under 25 were under-represented. Conversely, men and women over 65 were over represented in the sample. This pattern of lower age groups being under-represented was generally repeated across each of the Health Boards as shown in Table 1.11.

Tables 1-4-1.6, Table 1.9 and Table 1.11

1.6.4 Individual response for children (0-15)

Interviews were undertaken with 1,787 children aged 0 to 15, with 847 interviews taking place as part of the main sample and 940 as part of the child boost.

As was the case with the adult sample, in order to calculate the response rate for children, the number of eligible children in selected households (the "set" sample) had to be estimated. This was done by assuming that, for both the main sample and the child boost sample, the non-responding and responding households contained the same average number of children.

Table 1.7 shows that overall response rates for both the main sample and the child boost were the same for boys and girls with a response rate of 58% for the main sample and 69% from the child boost sample.

Child response rates have also been calculated for children in responding households. Table 1.8 shows that for age groups under 11 years old the response rate for boys and girls was fairly consistent at over 94% for every group, however, the response rate for children aged 11 to 15 was slightly lower at 88% for both boys and girls.

Table 1.10 shows that the overall child sample provided a good representation of the child population in terms of age groups as the proportion in each age group for the sample and NRS population estimates were very similar. Tables 1.7, 1.8 and 1.10

1.7 Weighting the Data

1.7.1 Introduction

This section presents information on the weighting procedures applied to the survey data. For 2012 the weighting was undertaken by the Scottish Government rather than the survey contractor (as had previously been the case), but the methodology applied was largely consistent with that from the 2008 to 2011 sweeps of the survey. The procedures for the implementation of the weighting methodology were developed by the Scottish Government working with the Methodology Advisory Service at the Office for National Statistics.[8]

To undertake the calibration weighting the ReGenesees Package for R was used and, within this, to execute the calibration, a raking function was implemented.

1.7.2 Main adult weights

The main adult weight is applicable for all adults interviewed as part of the main sample and the Health Board boosts. There were six steps to calculating the overall adult weights. These were as follows:

Address selection weights (w1)
The address selection weights were calculated to compensate for unequal probabilities of selection of addresses in different survey strata. For the main sample combined with the Health Board boost there were 36 strata overall (one for each local authority, an extra strata for the Lanarkshires and two extra strata in Fife as a result of the boost). The address selection weight for each stratum was calculated as:

Address selection weights (w1)

Dwelling unit selection weights (w2)
As stated in Section 1.2.7, the MOI for the PAF was used to ensure that if there were multiple dwelling units at a single address point they would have the same selection probability as individual addresses. However, there were some cases where the MOI was incorrect. The following correction was applied where this was the case:

Dwelling unit selection weights (w2)

With w2 trimmed to a maximum of 3.

Household selection weights (w3)
Similarly, within a very small number of dwelling units fieldworkers found multiple households, of which only one was selected for participation in the survey. The following correction was applied for multiple households:

Household selection weights (w3)

With (w3) trimmed to a maximum of 3.

Calibrated household weights (w4)
The three selection weights were combined (w1*w2*w3) prior to the household calibration stage. This combined weight was applied to the survey data to act as entry weights for the calibration. The execution of the calibration step then modified the entry weights so that the weighted total of all members of responding households matched the population totals for Health Boards, Scotland-level population totals for age/sex breakdown, and the population within SIMD15 areas. The population totals were used were the National Records of Scotland's (NRS) mid-2011 estimates for private households[9]. Figures 1I - 1K show the target populations.

Adult non-response weights (w5)
All adults within selected households were eligible for interview, but within responding households not all individuals completed an interview. The profiles of household members that did not complete the interview were different from those that did. Information on all individuals within responding households was available through information gathered as part of the household interview. This allowed the differential response rates for individuals within households to be modelled using logistic regression to calculate a probability of responding based on their profiles. The logistic regression was only applicable for households containing more than one adult since households consisting of only one adult either responded to the household and individual interviews or did not respond at all.

The following variables were considered for inclusion in the model:

  • Health Board
  • Age/sex
  • Number of adults in the household
  • Employment status of household reference person
  • Presence of a smoker in the household
  • Frequency of eating meals together
  • Marital status
  • Tenure
  • Urban/rural classification
  • Access to a car
  • Located within SIMD15 area

Through running backwards and forwards selection procedures for the logistic regression the following variables were included in the final model:

  • Health Board
  • Age/sex
  • Number of adults in the household
  • Frequency of eating meals together
  • Marital status
  • Urban/rural classification
  • Access to a car
  • Located within SIMD15 area

The final logistic regression model was then used to calculate the probability of response for all individuals that did respond. The adult non-response weight (w5) was then calculated as the reciprocal of this probability:

The adult non-response weight (w5)

For households of only one adult the non-response weight was one.

Individual calibration and final adult weight (int12wt)
The household (w4) and non-response (w5) were combined (w4*w5) and applied to the survey data prior to the final stage of calibration weighting which matched weighted totals for the survey data to the NRS 2011 mid-year population estimates for Health Boards, age/sex distribution at Scotland level and age/sex distribution for the Greater Glasgow & Clyde Health Board.

Figure 1I: 2011 Mid-year population estimates for private households in Scotland by Health Board

Health Board Children Adults Total
Ayrshire & Arran 62,920 299,880 362,800
Borders 19,730 92,360 112,080
Dumfries & Galloway 24,240 122,140 146,370
Fife 64,860 295,270 360,140
Forth Valley 53,570 234,720 288,290
Grampian 96,330 445,510 541,840
Greater Glasgow & Clyde 208,380 980,690 1,189,070
Highland 52,780 253,240 306,010
Lanarkshire 105,350 452,840 558,200
Lothian 142,090 685,990 828,080
Orkney 3,320 16,610 19,960
Shetland 4,180 18,030 22,200
Tayside 67,880 326,900 394,780
Western Isles 4,360 21,480 25,830
Total 909,990 4,245,660 5,155,650

Total figures might not be exact due to rounding

Figure 1J: 2011 Mid-year population estimates for private households in Scotland by SIMD15 indicator

SIMD15 Total population
15% most deprived datazones 737,719
All other datazones 4,417,931
Total 5,155,650

Total figures might not be exact due to rounding

Figure 1K: 2011 Mid-year population estimates for private households in Scotland by age group

Age group Male Female Total
0-4 151,310 145,347 296,657
5-9 139,220 133,158 272,378
0-15 174,751 166,204 340,955
16-24 298,970 287,550 586,520
25-34 337,990 332,300 670,290
35-44 335,500 365,380 700,880
45-54 370,270 402,150 772,420
55-64 319,520 337,250 656,770
65-74 221,450 253,430 474,880
75+ 152,370 231,530 383,900
Total 2,501,351 2,654,299 5,155,650

Total figures might not be exact due to rounding

1.7.3 Biological module weights

A similar process was applied to derive the weights for the biological module. This is outlined below.

Address selection weight (bw1)
New address selection weights were calculated using the same process as described for w1 but with the Health Board boost addresses excluded.

Dwelling unit (w2) and household selection weights (w3)
The dwelling unit and household selection weights from the main adult weight were applied as above.

Calibrated household weight (bw4)
The three selection weights were combined (bw1*w2*w3) and applied to the survey data before the household calibration was run so that survey data matched the population totals for Health Boards, Scotland-level age/sex breakdown, and the population within SIMD15 areas.

Adjustment for biological module selection (bw5)
Approximately one third of the main sample was allocated to the biological module. To incorporate this probability of selection a correction was applied to the calibrated household weight (bw4). The correction was:

Adjustment for biological module selection (bw5)

Application of adult non-response (w5)
For within household non-response, the non-response weight (w5) calculated for all households was also applicable for the biological module.

Non-response weight for biological module interview
Not all of the adults that responded to the main section of the interview responded to the biological module. Using the information collected for the respondent in the main interview and household interview the likelihood of responding to the biological module was modelled with logistic regression. The following variables were considered for inclusion in the model:

  • Health Board
  • Age/sex
  • Number of adults in the household
  • Employment status of Household reference person
  • Presence of a smoker in the household
  • Frequency of eating meals together
  • Self-assessed general health
  • Gardening/DIY/building work in past 4 weeks
  • Any physical activity in past 4 weeks
  • Economic activity (working/retired/sick)
  • Any housework in past 4 weeks
  • Marital status
  • Tenure
  • Urban/rural classification
  • Access to a car
  • Located within SIMD15 area
  • Long-term illness or disability
  • Highest qualification held
  • Ever had high blood pressure
  • Current smoker
  • Currently drink alcohol
  • Number of natural teeth
  • Any barriers to entry to the property

Through running backwards and forwards selection procedures for the logistic regression the following variables were included in the final model for response to the biological module:

  • Health Board
  • Age/sex
  • Number of adults in the household
  • Frequency of eating meals together
  • Self-assessed general health
  • Marital status
  • Located within SIMD15 area
  • Long-term illness or disability
  • Highest qualification held

The final logistic regression model was then used to estimate the probability of response for all individuals that did respond to the biological module. The biological module non-response weight (bw6) was then calculated as the reciprocal of this probability:

The biological module non-response weight (bw6)

Final calibration for biological module (bio12wt)
The household (bw4), biological sample correction (bw5), adult non-response (w5), and biological non-response (bw6) weights were combined (bw4*bw5*w5*bw6) and applied to the survey data.

For the final stage of biological module weighting the weighted totals for the survey data were calibrated to match the NRS 2011 mid-year population estimates for Health Boards, age/sex distribution at Scotland level. However, due to the low sample size for the module a number of the categories had to be collapsed. In terms of Health Boards, all areas except for Grampian, Greater Glasgow and Clyde, Highland, and Lanarkshire were grouped together. For the age groups, the lowest two age groups were combined as were the highest two age groups.

1.7.4 Non-biological module weights (Version A)

A weight titled "Version A" was calculated for the individual respondents in the main sample that were not selected for the biological module. This consisted of the main sample without the Health Board boost sample. The following steps were followed to derive the weight:

Address selection weight (bw1)
As derived in the first step of the biological module weight.

Dwelling unit (w2) and household selection weights (w3)
The dwelling unit and household selection weights from the main adult weight were applied as above.

Calibrated household weight (bw4)
As derived for the biological module.

Adult non-response weight (w5)
For within household non-response, the non-response weight (w5) calculated for all households was also applicable for the biological module.

Final calibration for Version A weight (vera12wt)
The household (bw4) and adult non-response (w5) weights were combined (bw4 *w5) and applied to the survey data. As was the case with the main adult weight and biological module weight, the weighted totals for the survey data were calibrated to match the NRS 2011 mid-year population estimates for Health Boards, age/sex distribution at Scotland level.

1.7.5 Overall child weights

An overall child weight was derived for child responses from the main sample and from the child boost combined. Separate logistic regression non-response weights were not required for the child samples as the response rate for children within cooperating households was sufficiently high at 94%. The weighting steps are shown below. The first two steps followed the same process as described in Section 1.7.2

Address selection weight for main sample and child boost combined (cw1)

Dwelling unit (cw2) and household (cw3) selection weights

Selection of children within each household (cw4)
A maximum of two children were eligible for interview in each household. To ensure that children in larger households were not under-represented in the final sample the following child selection weight was calculated for households with more than two children to compensate for the probability of selection:

Selection of children within each household (cw4)

For households with two or less children cw4=1.

Calibration for child interview weight (cint12wt)
The address selection (cw1), dwelling unit (cw2), household (cw3) and child selection weights (cw4) were combined (cw1*cw2*cw3*cw4) and applied to the survey data. The weighted totals for the survey data were calibrated to match the NRS 2011 mid-year population estimates for Health Boards, age/sex distribution at Scotland level.

1.7.6 Main sample child weights

Some analysis can only be undertaken on child responses from the main sample. Therefore, a separate child weight is required for this subset of child responses. The steps were the same as those for the overall child weights:

Address selection weight for main sample (mcw1)

Dwelling unit (cw2) and household (cw3) selection weights

Selection of children within each household (cw4)

Calibration for main sample child interview weight (cvera12wt)
The address selection (mcw1), dwelling unit (cw2), household (cw3) and child selection weights (cw4) were combined (mcw1*cw2*cw3*cw4) and applied to the survey data. The weighted totals for the survey data were calibrated to match the NRS 2011 mid-year population estimates for Health Boards, age/sex distribution at Scotland level. Due to the low sample size of children from the main sample most of the Health Boards had to be grouped together - only Greater Glasgow and Clyde and Lothian were kept separate.

1.8 Data Analysis and Reporting

SHeS is a cross-sectional survey of the population. It examines associations between health states, personal characteristics and behaviour. However, such associations do not necessarily imply causality. In particular, associations between current health states and current behaviour need careful interpretation, as current health may reflect past, rather than present, behaviour. Similarly, current behaviour may be influenced by advice or treatment for particular health conditions.

1.8.1 Reporting age variables

Defining age for data collection

A considerable part of the data collected in the 2012 SHeS is age specific, with different questions directed to different age groups. During the interview the participant's date of birth was ascertained. For data collection purposes, a participant's age was defined as their age on their last birthday before the interview.

Age as an analysis variable

Age is a continuous variable, and an exact age variable on the data file expresses it as such (so that, for example, someone whose 24th birthday was on January 1 2012 and was interviewed on October 1 2012 would be classified as being aged 24.75 (24¾)).

The presentation of tabular data involves classifying the sample into year bands. This can be done in two ways, age at last birthday and 'rounded age', that is, rounded to the nearest integer. In this report all references to age are age at last birthday.

Age standardisation

Some of the adult data included in the 2012 report have been age-standardised to allow comparisons between groups after adjusting for the effects of any differences in their age distributions. If data reported has been age-standardised this is highlighted in the title to the table or chart. When different sub-groups are compared in respect of a variable on which age has an important influence, any differences in age distributions between these sub-groups are likely to affect the observed differences in the proportions of interest.

It should be noted that all analyses in the report are presented separately for men and women and on some occasions data for all adults are also presented. All age standardisation has been undertaken separately within each sex, expressing male data to the overall male population and female data to the overall female population. When comparing data for the two sexes, it should be remembered that no age standardisation has been introduced to remove the effects of the sexes' different age distributions.

Age standardisation was carried out using the direct standardisation method. The standard population to which the age distribution of sub-groups was adjusted was the mid-year 2011 household population estimates for Scotland.9 The age-standardised proportion p' was calculated as follows, where pi is the age specific proportion in age group i and Ni is the standard population size in age group i:

The age-standardised proportion p'

Therefore p' can be viewed as a weighted mean of pi using the weights Ni. Age standardisation was carried out using the age groups: 16-24, 25-34, 35-44, 45-54, 55-64, 65-74 and 75 and over. The variance of the standardised proportion can be estimated by:

The variance of the standardised proportion

1.8.2 Standard analysis breakdowns

National Statistics Socio-Economic Classification (NS-SEC)

SHeS 2012 measured socio-economic status using the National Statistics Socio-Economic Classification (NS-SEC) which was introduced in 2001. NS-SEC was introduced to SHeS in 2003 and replaced the social class measures used in the two previous rounds of survey, Registrar General's Social Class (SC) and Socio-economic Group (SEG).[10]

NS-SEC was classified in two ways: on the basis of participants' own current or most recent occupation, and on the basis of the occupation details of the household reference person. The household reference person (HRP) was defined as the householder (the person in whose name the property was owned or rented) with the highest income. If there was more than one householder and they had equal incomes, then the household reference person was the eldest. The identity of the HRP was established in the household questionnaire and details about their occupation were collected at this point. If the HRP occupational details were collected by proxy from another household member these were collected again directly from the HRP during their individual interview (if one took place). Children were assigned the NS-SEC value of the HRP.

NS-SEC is an occupational based classification that uses the Standard Occupational Classification 2000 (SOC 2000) which replaced the Standard Occupational Classification 1990 (SOC 90) schema. The combination of SOC 2000 and information collected about employment status (whether an employer, self-employed or employee; whether a supervisor; number of employees at the workplace) for current or last job generates the following NS-SEC analytic classes:

  • Employers in large organisations, higher managerial and professional
  • Lower professional and managerial; higher technical and supervisory
  • Intermediate occupations
  • Small employers and own account workers
  • Lower supervisory and technical occupations
  • Semi-routine occupations
  • Routine occupations.

The remaining categories include those who have never worked, or who gave no occupational details or whose information was inadequately described or unclassifiable for other reasons. The analysis in the 2012 report was based on a five level version of this classification which combined the first two groups and the last two. Analysis is also possible using a three level classification which combines the intermediate and small employers and own account worker categories, and combines the lower supervisory group with the routine categories. All analysis was conduced using the NS-SEC of the HRP.

NS-SEC is a conceptually based schema which was developed from a sociological classification, the Goldthorpe Schema.[11],[12] The measure used in the 1995 and 1998 surveys, SC, used levels of occupation skill as the basis for its classification, whereas NS-SEC aims to differentiate between positions in the labour market in terms of aspects such as sources of income, job security, career advancement, authority and autonomy. A version of SC, derived from NS-SEC, has been produced by the Office for National Statistics and is available on the dataset.

Household income

The 2012 survey included questions designed to measure participants' household income. While household income alone can be used as an analysis variable, the analysis conducted for this report used an adjusted measure which took account of the number of persons within the household. The McClements method was used to equivalise incomes; this is detailed in the Glossary at the end of this report. The equivalised income measure was divided into quintiles for the presentation of analysis within the report, but the full continuous data is available on the dataset.

Scottish Index of Multiple Deprivation (SIMD)

The analysis was based on the 2012 version of the Scottish Index of Multiple Deprivation.[13] It is based on 38 indicators in seven individual domains of current income, employment, housing, health, education, skills and training, geographic access to services and crime. SIMD is calculated at data zone level, enabling small pockets of deprivation to be identified. The data zones are ranked from most deprived (1) to least deprived (6505) on the overall SIMD index. The result is a comprehensive picture of relative area deprivation across Scotland. The index was divided into quintiles for the presentation of analysis within the report, a version divided into deciles is also available on the dataset. The full index is not available on the archived dataset due to concerns about its potential for identifying individual respondents or households.

1.8.3 Regression

Regression modelling has been used in two of the chapters, to examine the factors associated with selected outcome variables, after adjusting for other predictors. For instance, in Chapter 3, binary logistic regression analyses have been performed to examine the association between Alcohol Use Disorder Identification Test scores (AUDIT), and a variety of predictor variables, including age, household income, marital status, and being a parent. Models were run for men and women separately. Chapter 9 also uses binary logistic regression to examine the association between being a problem gambler and various predictor variables. A wide range of possible predictor variables were tested in each model. This gives an estimate of the independent effect of each predictor variable on the outcome when all the other independent variables were included in the model.

The results of the binary logistic regression analyses are presented in tables showing odds ratios for the final models, together with the probability that the association is statistically significant. The predictor variable is significantly associated with the outcome variable if p<0.05. The models show the odds of being in the particular category of the outcome variable (e.g. having an AUDIT score of 8 or above, displaying signs of an alcohol use disorder (AUD)) for each category of the independent variable (e.g. quintiles of equivalised household income). Odds are expressed relative to a reference category, which has a given value of 1. Odds ratios greater than 1 indicate higher odds, and odds ratios less than 1 indicate lower odds. Also shown are the 95% confidence intervals for the odds ratios. Where the interval does not include 1, this category is significantly different from the reference category.

Missing values were included in the analyses, that is, people were included even if they did not have a valid answer, score or classification in one or more of the explanatory variables. Where this was a large number of people, the missing values were included as a separate category (e.g. income), and where there were few records with a missing value, these individuals were included with the category containing the largest number of cases (e.g. economic status).

1.8.4 Design effects and true standard errors

SHeS 2012 used a clustered, stratified multi-stage sample design. In addition, weights were applied when obtaining survey estimates. One of the effects of using the complex design and weighting is that standard errors for survey estimates are generally higher than the standard errors that would be derived from an unweighted simple random sample of the same size. The calculations of standard errors shown in tables, and comments on statistical significance throughout the report, have taken the clustering, stratification and weighting into account. The ratio of the standard error of the complex sample to that of a simple random sample of the same size is known as the design factor. Put another way, the design factor (or 'deft') is the factor by which the standard error of an estimate from a simple random sample has to be multiplied to give the true standard error of the complex design. The true standard errors and defts for SHeS 2012 have been calculated using a Taylor Series expansion method. The deft values and true standard errors (which are themselves estimates subject to random sampling error) are shown in Tables 1.12 to 1.20 for selected survey estimates presented in the main report Tables 1.12 to 1.20

References and notes

[1] Further information on the Scottish Health Survey review and recommendations adopted as a result of the review can be found on the Scottish Government SHeS website: www.scotland.gov.uk/Topics/Statistics/Browse/Health/scottish-health-survey

[2] Scotland's Population 2011 - The Registrar General's Annual Review of Demographic Trends 157th edition, Edinburgh: Scottish Government, 2012. Available from: www.gro-scotland.gov.uk/files2/stats/annual-review-2011/j21285200.htm

[3] Further information on the sample designs and the methodology uses is available here: http://scotland.gov.uk/Topics/Statistics/About/SurveyDesigns201215

[4] Intermediate geographies are geographic units defined by the Scottish Government. They are made up of around five datazones and there are 1,235 across Scotland. Further information on intermediate geographies is available here: www.scotland.gov.uk/Publications/2005/02/20732/53083

[5] www.ic.nhs.uk/pubs/psychiatricmorbidity07

[6] The household reference person (HRP) is defined as the householder (a person in whose name the property is owned or rented) with the highest income. If there is more than one householder and they have equal income, then the household reference person is the eldest.

[7] Lynn, Peter, Beerten, Roeland, Laiho, Johanna and Martin, Jean (October 2001) 'Recommended Standard Final Outcome Categories and Standard Definitions of Response Rate for Social Surveys', Working Papers of the Institute for Social and Economic Research, paper 2001-23. Colchester: University of Essex.

[8] A report on the development of the weighting procedures is available here: www.scotland.gov.uk/Topics/Statistics/About/Surveys/WeightingProjectReport

[9] 2011 estimates were used as the 2012 estimates were not available at the time the weighting was undertaken.

[10] Full details of the NS-SEC classification can be found at: <http://www.ons.gov.uk/ons/guide-method/classifications/current-standard-classifications/soc2010/soc2010-volume-3-ns-sec--rebased-on-soc2010--user-manual/index.html>

[11] Goldthorpe, J.H. (1997) 'The 'Goldthorpe' class schema: some observations on conceptual and operational issues in relation to the ESRC review of government social classifications' in D. Rose and K. O'Reilly (eds). Constructing Classes: Towards a New Social Classification for the UK. Swindon: ESRC/ONS.

[12] Goldthorpe, J.H. (with C. Llewellyn) (1980/1987) Social Mobility and Class Structure in Modern Britain. Oxford: Clarendon.

[13] www.scotland.gov.uk/Topics/Statistics/SIMD/Publications

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Email: Julie Landsberg

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