The Scottish Health Survey 2021 - volume 2: technical report
This publication pesents information on the methodology and fieldwork from the Scottish Health Survey 2021.
This document is part of a collection
Chapter 1: Methodology And Response
1.1.1 The Scottish Health Survey series
The Scottish Health Survey (SHeS) series was established in 1995 to provide data about the health of the population living in private households in Scotland. It was repeated in 1998 and 2003 and has been carried out annually since 2008.
The 2018-2023 surveys are being conducted by ScotCen Social Research in collaboration with the Office for National statistics (ONS), the Social and Public Health Sciences Unit (MRC/CSO SPHSU) at the University of Glasgow, the Centre for Population Health Sciences at the University of Edinburgh and the Public Health Nutrition Research Group at the University of Aberdeen .
Fieldwork for the 2020 and 2021 surveys were significantly affected by the COVID-19 pandemic. Fieldwork for SHeS 2020 was suspended in March 2020. Data for some of the key measures from SHeS was collected via a telephone survey in August and September 2020. Due to the testing of a new methodology for the SHeS survey within the context of the COVID-19 pandemic, the survey results for 2020 were presented as experimental statistics. These results have not been included in Volume 1 of this report.
1.1.2 The SHeS 2021 Fieldwork
There were two phases of fieldwork for SHeS 2021. During Phase 1, potential participants were contacted by letter and asked to opt-in to taking part in an interview conducted over the phone. This phase began in April, with new invites being sent out each month until September 2021. The survey itself was more comprehensive than 2020, with similar content to earlier survey years, and unlike 2020, interviews with or on behalf of children were also conducted.
Phase 2 began at the end of October, with new sample issued across three months. Potential respondents were again contacted by letter, but then recruited to participate by interviewers knocking on their door, in what is termed a ‘knock-to-nudge’ methodology. Interviews were still conducted by telephone, as for Phase 1. This second phase only began once COVID-19 restrictions in Scotland had been lifted to the extent that Scottish Government ministers and the Chief Medical Officer gave permission for such doorstep contact to recommence on Scottish Government surveys. The shift to a knock-to-nudge approach significantly increased levels of response to the survey.
Participants from the child boost sample were invited to opt in via letter for the entire fieldwork period.
The telephone survey methods differed from those used prior to 2020 in the SHeS series. While the 2021 survey includes most of the questions and key indicators from the face-to-face surveys, the change in mode of administration, along with the different approach to sampling, is likely to have impacted the responses received and thus comparability with the previous SHeS data. See sections 1.1.5, 1.1.7 and 1.2 for more information.
1.1.3 Aims of the Scottish Health Survey
The purpose of SHeS is to provide information at national level about the health of the population and the ways in which lifestyle factors are associated with health. This level of information is not available from administrative or operational databases, as hospitals and GPs are not able to collect detailed information about peoples’ lifestyles and health- related behaviours. In addition, it is crucial that the Scottish Government has information about the health of the population, including people who do not access health services regularly.
The specific aims of SHeS are:
- To estimate the prevalence of particular health conditions in Scotland.
- To estimate the prevalence of certain risk factors associated with these health conditions and to document the pattern of related health behaviours.
- To look at differences between regions and between subgroups of the population in the extent of their having these particular health conditions or risk factors, and to make comparisons with other national statistics for Scotland and England.
- To monitor trends in the population’s health and health related behaviour over time.
- To make a major contribution to monitoring progress towards health targets.
Each survey in the SHeS series has a set of core questions and measurements (height and weight and, if applicable, blood pressure, waist circumference, and saliva samples), plus modules of questions on specific health conditions and health risk factors that vary from year to year. Each year the main sample has been augmented by an additional boosted sample for children.
The purpose of the SHeS 2021 survey was to provide this same information at national level in the context of the developing COVID-19 pandemic. The SHeS series now has trend data going back 26 years and providing this time series is an important function of the survey.
1.1.4 Key changes to the survey methodology in 2018
A number of changes were introduced in light of the 2017 Scottish Government review of the Scottish Surveys Core Questions (a set of harmonised core questions asked across the three major Scottish Government household surveys), and following the 2016 Scottish Government consultation on the Scottish Health Survey questionnaire content. The key changes implemented in 2018 for the 2018-2021 surveys include:
- Increased sample size allowing for analysis at Local Authority level by 2021.
- Removal of local police force, contraception and cosmetic procedures questions.
- Removal of urine sample from the biological module.
- A number of modules will no longer appear in the questionnaire each year, but will appear approximately every 2 or 4 years: gambling, problem drinking, dental health services, parental history, respiratory health, CPR training and use of health services.
- New questions introduced asked about satisfaction with key public services, Nicotine Replacement Therapy (NRT), asthma, type of diabetes and gender identity.
- Additional topics were introduced in 2019 and 2021.
These changes are discussed in greater detail in section 1.3 below and also in the Scottish Health Survey Report of Questionnaire Changes from 2018.
1.1.5 The 2021 survey
The 2021 Scottish Health Survey was designed to provide data at national level about the population living in private households in Scotland. The survey covered all ages.
The target sample size for the 2021 survey was the same as that for 2018 and 2019. Because of the requirement for telephone interviewing, with no doorstep recruitment allowed until the end of October, the issued sample was much larger than in previous years.
An initial sample of 64,523 addresses was drawn from the Postcode Address File (PAF) in 2021 on the basis of the survey being conducted by opt-in. These addresses comprised three sample types: main (core) sample version A, main (core) sample version B and the child boost screening sample. This sample was split into 9 monthly waves of fieldwork, from April to December. For the core samples, only the first 6 months were issued, as the sample was superseded by a smaller knock-to-nudge sample for the final three months (the sample for knock-to-nudge was smaller due to higher expected levels of response for this approach). The child boost sample was used for the whole 9 months.
Replacement core sample (3,839 addresses) was drawn for the last three months of 2021 to be issued as knock-to-nudge.
For Phase 1 of the survey, participants were asked to opt-in using an online portal, or by contacting the NatCen freephone team. They were asked to leave a telephone number on which an interviewer would call them back. Addresses were only assigned to interviewers after the household had opted into the survey. Assignments comprised up to 10 addresses and a mix of all sample types.
For Phase 2 of the survey, the 3,839 addresses were grouped into 134 interviewer assignments, with around 44 assignments being issued to interviewers each month between October and December 2021.
ScotCen Social Research enlisted the Office for National Statistics (ONS) to assist with the interviewing for the duration of the 2018-2023 contract. ONS interviewers were only used for the knock-to-nudge element of the 2021 survey. As a result, ONS were allocated approximately 30% of the sampled knock-to-nudge addresses.
The table below shows the total number of addresses (mainstage and additional) issued for each sample type and the people eligible for interview within each sample type.
|Sample type||Number of addresses issued in 2021||Eligible for interview|
|Core version A||13,859 opt-in 2,290 K2N||Max of 10 adults (age 16+) and 2 children (age 0-15)|
|Core version B||9,253 opt-in 1,549 K2N||Max of 10 adults (age 16+) and 2 children (age 0-15)|
|Child boost||29,833 opt-in||Only households containing children aged 0-15 were eligible to participate (up to two children at these households were eligible to be interviewed)|
Data collection involved a main computer assisted telephone interview (CATI), and online or paper self-completion questionnaire.
As interviews were conducted by telephone, no height and weight measurements or biological measures could be taken. Participants were asked to estimate their own height and weight during the interview. In previous years, the core version B sample completed a biological module, and these addresses were only assigned to trained bio interviewers. For 2021, as no biological measurement could be taken the only real differences between the core version A and version B interviews were a slightly longer telephone interview for version A to cover the rotating modules and a slightly longer self-completion for version B to cover the depression, anxiety, self-harm and attempted suicide questions which are included in the biological module.
Participants aged 16 and above were also invited to complete an online recall using Intake24 (https://intake24.org/). Participants were asked to provide verbal consent, which was recorded in CAPI. Respondents were also sent a leaflet with some key information about Intake24 included. If the respondent indicated to the interviewer that they had not read the Intake24 information leaflet (sent with their advance letter), the interviewer read out key information from this before obtaining consent. Those who agreed were invited to complete two dietary recalls, either independently or via a phone call with Cambridge University. Further information about Intake24 is provided in sections 1.3.7, 1.6.5, 1.7.7 and 1.8.4.
1.1.6 The 2021 SHeS annual report
The 2021 report consists of two volumes, published as a set under ‘The Scottish Health Survey 2021’. Volume 1 presents results for adults and children on a variety of health topics. This report (Volume 2) provides methodological information and survey documentation. Both volumes are available on the Scottish Government’s website along with a short summary report of the key findings from the 2021 survey (Scottish Health Survey). Supplementary web tables are also available on this website. These provide a large number of breakdowns by age group, deprivation, income and limiting long-term conditions. An interactive dashboard is also available presenting key indicators for Scotland, NHS Boards and local authority areas.
1.1.7 Comparisons with previous surveys in the SHeS series
In the 2021 report comparisons are made with data collected earlier in the series (1998-2019 for children and 2003-2019 for adults). However, it should be noted that, due to the difference in method for 2021, caution should be applied when comparing results from this survey year to those for previous years. Caution is advised due to:
- The use of an opt-in approach resulting in a lower proportion of respondent households in the most deprived areas and a lower proportion of respondents in the youngest age group than in previous survey years. Interviews achieved as part of the knock-to-nudge sample brought the overall achieved sample a bit closer to the profile in previous years. The weighting strategy adjusted the results to be representative of the household population as a whole as far as possible.
- Changes in the mode of survey administration to telephone with knock-to-nudge recruitment including:
- The use of self-reported height and weight data in place of objective measurements taken by interviewers. Whilst for adults an adjustment has been made for this, the mode of data collection requires the continued use of caution when interpreting such data.
- Changes to the way the respondents answer some questions including the potential for greater honesty when providing potentially sensitive information
- Reduced opportunity to build interviewer rapport
- Changes to the sampling approach such as the use of an unclustered sample during phase 1 of fieldwork.
In addition, this report includes analysis from some combined datasets: one for the years 2017 to 2021 combined and one for the years 2019 and 2021 combined to aid analysis of small subsamples of the population and/or for questions which are included in the survey every second year. Combining data across years in this way allows for a more detailed analysis of subgroups in the sample and allows for analysis of questions with small sample sizes in one survey year.
1.1.8 Health Board and local authority level analysis
Since 2008, the SHeS sample has been designed to be representative of adults at Health Board level (for all Health Boards) following four years of data collection and in 2018 the sample size was increased to allow analysis by local authority. Analysis of the 2017 to 2021 data by NHS Health Board and by local authority is published at the same time as this report, and is available on the SHeS website (Scottish Health Survey). Areas with larger samples may be able to analyse data at their area level based on fewer years of data collection and users should consult the SHeS website for further guidance on sub-geographies analysis.
Changes in the sample design for the 2012 survey mean that users are not advised to combine data for periods spanning 2011 and 2012. Since 2012, however, the sample has been designed to be representative of the population of Scotland at Health Board level for every four-year period. Hence the survey can be analysed using combined data from 2012 to 2015, 2013 to 2016, 2014 to 2017, 2015 to 2018, 2016 to 2019 or 2017 to 2021. It should be noted that no data for 2020 is available by Health Board.
1.1.9 Access to SHeS data
Data from the 2021 survey will be deposited at the UK Data Service along with a combined 2017-2021 dataset and a combined 2019/2021 dataset. Datasets from earlier years in the series are also deposited here (www.ukdataservice.ac.uk).
1.2 Sample Design
The sample specification for the 2021 SHeS was designed by the Scottish Government. The design was coordinated with the designs for the Scottish Household Survey (SHS) and the Scottish Crime and Justice Survey (SCJS) to improve survey efficiency and to allow the samples of the three surveys to be pooled for further analysis.
There were two elements to the SHeS sample in 2021:
1) Main adult sample - to allow annual reporting of Scotland level results and results at Health Board and local authority level using the 2017, 2018, 2019 and 2021 data combined. This required an annual interview target of 5,112 adults for Scotland as a whole and a minimum of 125 for each local authority. There was an additional requirement for a minimum of 1,000 adults to complete each biological measure each year.
2) Child sample boost – overall there was a requirement for 2,031 child interviews for Scotland. As the main sample was only expected to yield 1,026 child interviews, a further 1,005 interviews were required from a separate boost sample.
1.2.2 Sample design and assumptions
In 2021, the opt-in and knock-to-nudge samples utilised different sampling approaches. The opt-in approach did not require clustering as participants were not visited on the doorstep and interviews could be undertaken by interviewers located throughout Scotland.
For knock-to-nudge, the usual two-stage clustered sample design with intermediate geographies randomly selected at the first stage and address points at the second stage, was used. With the exception of Orkney, Shetland and Na h-Eileanan Siar councils, the sample was clustered by intermediate geographies (IG) with one quarter of IGs selected for each year of fieldwork. In Orkney, Shetland and Na h-Eileanan Siar the sample was clustered by data zone.
1.2.3 Main sample
As stated above, the annual sample size for Scotland was 5,112 adults with a minimum local authority sample size of 125 adults. These sample sizes were the minimum required to allow effective reporting of Scotland-level results annually and Health Board and local authority results with four years of data combined. An iterative approach was taken to efficiently allocate the sample across all Health Boards and local authorities. For the first iteration 4,000 adult interviews were allocated across local authorities in proportion to the adult population. Any local authorities allocated fewer than 125 adult interviews had their allocation increased to 125.
The remaining sample was then allocated over the remaining local authorities. Where allocations were not whole numbers the number was rounded up. This resulted in a total target of 5,112 adult interviews. The results of the allocation are shown in Table 2.
|Health Board||Target Annual Adult Interviews|
|Ayrshire and Arran||375|
|Dumfries and Galloway||125|
|Greater Glasgow and Clyde||1,075|
To allow for reporting at local authority level over a four-year period (2017/2018/2019/2021) and coordination with the sample selection of the SHS and SCJS, the required sample sizes were set at local authority level. This was done by allocating the target Health Board samples to local authorities proportionate to population.
The number of addresses selected in order to provide the target number of interviews for the opt-in part of the sample was calculated by:
1) Estimating the number of productive adult interviews per co-operating household. Considering response data from the shorter 2020 telephone survey, it was estimated that there would be an average of 1.3 interviews per co-operating households in each local authority.
2) Allocation of the target interviews and associated estimate of co-operating households to local authority strata proportionate to population.
3) The response rate assumptions for local authorities for 2021 were then estimated based on the variation across local authorities in response to the 2020 telephone survey and the 2018 and 2019 face-to-face surveys.
4) The final step was to estimate the level of ineligible addresses. As for previous survey years, the estimates were calculated at local authority level and based on the average level of ineligible addresses from previous years of SHeS, SHS and the SCJS.
For the knock-to-nudge part of the sample, a similar process was followed adjusting to account for a higher assumed response rate and a shorter period of fieldwork.
Tables 4 and 5 show the number of selected addresses used for the main sample in 2021 for opt-in and knock-to-nudge.
1.2.4 Child boost sample
For the 2021 survey, 2,031 child interviews were required. It was estimated that the opt-in and knock-to-nudge main sample would provide 1,026 child interviews, therefore, to reach the target number of child interviews, a child boost sample was required to yield a further 1,005 interviews.
The process for calculating the number of addresses to select for the child boost sample was as follows:
1) The child boost sample of 1,005 child interviews was allocated proportionally to local authorities based on the child (under 16) population. If the number expected from the child boost was less than 10, then the local authority boost target was set to zero. The following table shows the target sample sizes for the main sample and child boost sample by Health Board.
|Expected child interviews from main sample||Child interviews from boost||Total child interviews|
|Ayrshire and Arran||75||70||149|
|Dumfries and Galloway||25||27||50|
|Greater Glasgow and Clyde||219||216||427|
2) The number of co-operating households with children required in each Health Board for the child boost sample was estimated using the performance of the child boost samples in the surveys between 2013 and 2015.
3) To estimate the proportion of child-less households, data from child boost samples between 2012 and 2015 was used. As there was little variation across different areas a Scotland level estimate of households without children (80%) was used.
4) The assumptions made on ineligible addresses for the main sample were applied to the address calculations for the child boost sample.
The total numbers of addresses issued for the child boost sample are shown in Table 4.
|Sample strata||Main sample (inc. additional)||Child boost||Total sample|
|Argyll & Bute||573||444||1017|
|Dumfries & Galloway||490||680||1170|
|Edinburgh, City of||1385||2059||3444|
|Perth & Kinross||594||856||1450|
|Sample strata||Main adult sample|
|Argyll & Bute||108|
|Dumfries & Galloway||94|
|Edinburgh, City of||279|
|Perth & Kinross||97|
1.2.5 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 can be used to inform assumptions for 2021 sample design.
- It has excellent coverage of addresses in Scotland.
- The small user version excludes the majority of businesses.
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 SHS, SHeS and SCJS have all been selected by the Scottish Government since 2012, addresses selected for any of the surveys are removed from the sample frame so that they cannot be re-sampled for another survey. This helps to reduce respondent burden. The addresses are removed from the sample frame for a minimum of four years.
The sample design specified in Section 1.2 for opt-in was implemented in two stages:
1. The required numbers of addresses for the main and child boost samples were combined to give an overall total of addresses to sample for each stratum (local authorities). The required number of addresses for each stratum was then sampled from the sample frame of addresses. Systematic random sampling was used with addresses within PSUs ordered by urban-rural classification, SIMD rank and postcode.
2. Once the overall sample was selected, each address was randomly allocated to the main or the child boost sample. Also, one quarter of the target main adult sample was required to complete the biological module. To guard against a lower response rate to the different elements of the biological module, and to correct for inaccurate response assumptions in previous years, a proportion higher than the required one quarter of the main adult sample (40% in 2021) were allocated to the biological module.
The sample design specified in Section 1.2 for knock-to-nudge was implemented in three stages:
1. All primary sampling units (data zones on the islands, intermediate geographies elsewhere) were randomly allocated to one of four sets. One of these sets will be used in each in each year of fieldwork. This means that the sample is drawn from one quarter of PSUs each year. The sets were updated ahead of the 2021 sampling and this ensures that over four years of fieldwork (2021 to 2024) all addresses will have a non-zero probability of selection.
|Health Board||PSUs in 2021 Sample||Total PSUs|
|Ayrshire and Arran||24||93|
|Dumfries and Galloway||10||40|
|Greater Glasgow and Clyde||64||257|
2. As there was no child boost for the knock-to-nudge part of the sample, the required numbers of addresses for the main sample gave an overall total of addresses to sample for each stratum (local authorities). The required number of addresses for each stratum was then sampled from the sample 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, a proportion of the main sample addresses were randomly allocated to the biological module. One quarter of the target main adult sample was required to complete the biological module. To guard against a lower response rate to the different elements of the biological module, and to correct for inaccurate response assumptions in previous years, a proportion higher than the required one quarter of the adult sample (40% in 2021) were allocated to the biological module.
1.2.6 Selecting individuals within households
For the main sample, all adults aged 16 and over in responding households were eligible for interview. To ease respondent burden, for child interviews for both the main and the child boost samples a maximum of two children were interviewed at each household. If a household contained more than two children, then two were randomly selected for interview.
1.3 Topic coverage
Topics covered in the 2018 to 2021 surveys were agreed following a consultation carried out in 2016. Many of the topics and questions included in earlier years of the survey were included again to continue the time series, questions on long Covid were included for the first time. The 2021 survey included the same rotating topics as the 2019 and 2017 surveys (see sections 1.3.3 and 1.3.4), with the exception that the adverse childhood experience questions (ACES) were not asked in 2021 and questions on drug use were included for the first time. As with previous years, the 2021 survey had a focus on cardiovascular disease (CVD) and its associated risk factors.
The outcome of a public consultation about the content of the survey from 2018 is available from http://www.gov.scot/Resource/0053/00537370.pdf. This report outlines key changes to be made to the 2018-2021 surveys and other topics which would be considered if space became available.
Copies of all the documents used in data collection are included in Appendix A. Full copies of the questionnaire documentation used in the main interview and biological module are also available at Scottish Health Survey. A summary of the main interview content and the content of the biological module is provided below.
1.3.3 Main interview
Information was collected at both the household and individual level. Table 7 below summarises the content of the individual level interviews for all participants. The topics a participant was asked depended both on their age and the sample type to which their address had been allocated. The age criteria for each topic are included in brackets following the topic name.
Table 7: Content of the 2021 Interview
Main interview (asked of everyone)
Household questionnaire including household composition
General health including caring (0+)
Respiratory symptoms, cardiovascular disease and use of services (16+)
Physical activity adults (16+) and children (2-15)
Eating habits children (2-15)
Fruit and vegetables consumption (2-15)
Vitamins and supplements (0+)
Passive smoking (0+)
Dental health (16+)
CPR training (16+)
Employment and economic activity (16+)
Self-reported measurements (0+)
Ethnic background, religion and country of birth (0+)
Parental history/Family health (16+)
Accidents (0+) - Asked in version A of two thirds of the adult sample and Child Boost
Dental services (16+) - Asked in version A of two thirds of the sample only
Discrimination and harassment (16+) - Asked in version A of two thirds of the sample only
Stress at work (16+) - Asked in version A of two thirds of the sample only
Intake24 (16+) - Asked of those who agreed to take part in this follow up module
Table 8 Overview of topics included in SHeS adult self-completions
Self-completion – Adults aged 18+
Depression, anxiety, self-harm and suicide (only asked of those assigned to Version B – approximately a third of adults)
Non annual topics
Table 9. Overview of topics included in SHeS young adult self-completion booklets
Self-completion - Young adults
Depression, anxiety, self-harm and suicide (only asked of those assigned to Version B – approximately a third of adults)
Non annual topics
Table 10. Overview of topics included in 13–15-year-olds self-completion booklets
Self-completion - 13–15-year-olds
Table 11. Overview of topics included in 4–12-year-olds self-completion booklets
Self-completion - Parents of 4–12-year-olds
Strengths and difficulties questionnaire (SDQ)
Version A households accounted for 60% of the main (core) sample. At these households the questionnaire included the core questions and the questions included in the Version A rotating module. In 2021, the topics included in the Version A rotating module were: accidents, dental services, discrimination and harassment, stress at work, parental history and family health.
Version B households accounted for the remaining 40% of the main (core) sample. At these addresses, participants were asked the core questions during the main interview, with a slightly longer self-completion module that included depression, anxiety, self-harm and attempted suicide questions.
A significant number of changes were made to the questionnaire content in advance of the 2018 survey based on the consultation that took place in Autumn 2016, with a summary of responses published in Spring 2017. These changes are discussed below and in the Scottish Health Survey: Report of Questionnaire Changes from 2018.
From 2018, a number of modules were made less frequent and are no longer asked on an annual basis in the main interview but are asked biennially instead. These questions include those on family health and parental history, CPR training and use of health services.
There were also a few new questions added to the main interview in 2018. These include a question for those who have used a form of Nicotine Replacement Therapy (NRT) to aid smoking cessation, two questions concerning asthma; firstly, school absence due to asthma and secondly, treatment received for asthma, a question establishing whether respondents with diabetes have Type 1 or Type 2, and finally questions on respondents’ satisfaction with local services (for example local health services, local schools, refuse collection, public transport, council libraries, etc.).
A number of small amendments were also made to survey questions from 2018 (for example, updates to education qualifications). For full details of these please see the Scottish Health Survey: Report of Questionnaire Changes from 20188.
Significant changes were made to the child physical activity questions in 2017. These changes were designed to measure the activity guidelines of being physically active for at least 60 minutes per day for each day of the week (children aged 5 and over). This involved amending the questions. Previously, children were asked for the number of days on which they did physical activity and for the average amount of time this was for overall. The revised questions ask which days they did physical activity and the amount of time spent on each of those days (more information is provided in the Physical Activity chapter of the Main Report). These questions remained as they were for 2018.
Analysis of the 2017 data showed that it was not possible to derive a variable which would allow comparison between 2017 data (using the revised questions) and previous years of data (using the previous questions). For this reason, there is no trend analysis for children’s physical activity in 2017 or 2018. The question module used prior to 2017 was reinstated in the 2019 survey.
In 2021, questions on COVID-19 vaccinations and long COVID were included to monitor the continued effects of the pandemic on the health of those living in Scotland.
The full question wording of all the questions used in 2021 can be found at Scottish Health Survey.
1.3.4 Self-completion questionnaire
Participants aged 13 and over and parents of participants aged between 4 and 12 were asked to fill in a self-completion booklet during the interview. In all, four different booklets were administered. The version completed was dependent on the age of the participant.
The booklet for young adults aged 16-17 included questions on smoking and drinking behaviour (instead of these being asked as part of the CAPI interview). Interviewers also had the option of administering this young adults self-completion for those aged 18-19 if they felt that it would be more appropriate.
From 2018, some changes were made to self-completion booklets. Questions on contraception and cosmetic procedures were removed indefinitely from both the young adult and adult self-completion. Questions on problem drinking and gambling are now asked less frequently, with problem drinking questions asked biennially and gambling questions asked every few years. New questions on Adverse Childhood Experience were included in 2019 and questions on drug use were included for the first time in 2021.
From 2018, a new question on gender identity was added to the self-completion booklet. This question was added to both the young adult and adult self-completion booklets. For the wording of the questions in full, see the adult or young adult self-completion booklet listed at Scottish Health Survey .
Paper questionnaire booklets contained the following topics in the 2021 survey:
(Versions A & B) General Health Questionnaire (GHQ12), Warwick Edinburgh Mental Well-being scale (WEMWBS), food insecurity, problem drinking (AUDIT), drug use, gambling, social capital, food insecurity, loneliness, sexual orientation, and gender identity.
(Additional questions in version B) - depression, anxiety, self-harm and attempted suicide.
Smoking (including use of e-cigarettes), drinking, problem drinking (AUDIT), drug use, gambling, GHQ12, WEMWBS, social capital, food insecurity, loneliness, sexual orientation and gender identity.
13-15 year olds
GHQ12 and WEMWBS.
Parents of 4-12 year olds
Strengths and Difficulties questionnaire (SDQ)
(designed to detect behavioural, emotional and relationship difficulties in children).
1.3.5 Height and weight
Due to the restrictions in place at the time of the 2021 fieldwork, self-reported height and weight data was collected for participants aged 2 and over, with their consent.
1.3.6 Biological module
As highlighted previously, at a sub-sample (around 40%) of main core sample addresses, adults (aged 16 and over) were selected to complete the biological module. Since 2012, specially trained interviewers have been collecting the measurements and samples which were collected by nurses in previous years (1995 to 2011). This was not possible in 2021, therefore, no objective biological measurements were collected.
Participants in this sample were asked a set of questions about depression, anxiety, suicide attempts and self-harm (taken from the Adult Psychiatric Morbidity Survey) as part of their self-completion questionnaire. These questions were previously completed by the respondent using a computer-assisted self-completion approach (CASI) directly on to the interviewer’s laptop.
1.3.7 Intake24 dietary recalls
Respondents who consented to take part in Intake24 were invited to undertake dietary recalls on two separate occasions where they input details of their food and beverage consumption for the previous day. Two recalls, rather than a single recall, were requested to get a better understanding of an individual’s typical diet.
1.4 fieldwork procedures
1.4.1 Advance letters
Each sampled address was sent an advance letter that introduced the survey and for the knock-to-nudge sample, to let the resident know that an interviewer would be calling to seek permission to interview. A number of versions of the advance letter were used in 2021; one for the core version A addresses, one for core version B addresses (with the biological module), and one for child boost addresses. There was a version of each of these letters for each organisation conducting interviews (ScotCen Social Research and ONS), as well as for the opt-in and knock-to-nudge samples. 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.
For copies of the advance letters and survey leaflet, see the documents listed in Appendix A.
1.4.2 Making contact
Initial contact for both samples was made via the advance letter. For the opt-in sample, this letter provided instructions for taking part which involved contacting us via an online opt-in portal, the survey email address and/or the survey freephone number. Additional information was then sent by post to participants who opted in, which was followed by interviewer telephone contact to arrange a time to complete the interview.
The knock-to-nudge approach differed in that interviewers were able to visit respondent’s homes to attempt to obtain gain agreement to participate in the survey, which continued to be conducted by telephone. 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 1.2.7).
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) from the household. 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 randomly selected for interview. Interviewers obtained the verbal consent of both the parent/guardian and the child before commencing the interview.
1.4.3 Collecting data
Interviewers used computer assisted telephone interviewing (CATI) for the main SHeS interviews.
At each co-operating eligible household (across all sample types), the interviewer first completed a household questionnaire, with information collected from the household reference person or their partner wherever possible. This questionnaire obtained basic information (including date of birth and relationship to other household members) about all members of the household, regardless of age and whether they were eligible to take part in the interview. The computer assisted personal interviewing (CAPI) program then created individual questionnaires for each eligible participant in the household.
Where possible an individual interview was then conducted with all eligible adults and up to two children in a household. In order to reduce the amount of time spent in the home, interviews could be carried out concurrently.
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, and what will happen to information they provide (including a link to the Privacy Notice on the Scottish Government’s website).
A separate version of this leaflet was used for children in both main and child boost households. Parents at child boost addresses were also provided with a leaflet containing background information on the survey. Copies of all the participant leaflets used in the survey are included in Appendix A.
Online Intake24 dietary recalls were completed via a link (sent by text or email) sent directly to participants by the interviewer within minutes of giving consent. The second recall was completed within seven days of the initial recall. For participants who requested assistance to complete the recalls the interviewer collected a phone number and arranged an appointment date and time for the first recall for at least 5 days following the SHeS interview. This information was sent securely to the Cambridge University team. Participants opting for telephone assistance were sent a hard-copy food photograph atlas in advance to aid the estimation of portion sizes during completion of the dietary recalls. After the first recall was completed, the date for the second recall was arranged between the respondent and the caller from Cambridge.
1.4.4 Interviewing and measuring children
Children aged 13-15 were interviewed directly by interviewers, after verbal consent had been obtained from both the child and their parent or guardian. Interviewers were instructed to ensure that the child’s parent or guardian was present throughout the interview. Information about younger children (aged 0-12) was collected directly from a parent or guardian.
1.5 Fieldwork quality control and ethical clearance
1.5.1 Training interviewers
Interviewers new to SHeS were fully briefed on the survey’s content and procedures. Interviewers were supervised by an interviewer supervisor during the early stages of their work to ensure that interviews were administered correctly, and protocols were followed.
Interviewers that had worked on SHeS in previous years attended a refresher briefing ahead of the launch of the new survey year and were refreshed on the knock-to-nudge process when this was introduced. This ensured that they were aware of changes to survey content and procedures for 2021.
Interviewers interested in administering the biological module were initially screened for suitability. Minimum competency levels were set and only interviewers that met the set criteria were invited to training and accreditation sessions.
Full sets of written instructions, covering both survey procedures and measurement protocols, were provided to interviewers (measurement protocols are available on request from ScotCen Social Research).
1.5.2 Checking interviewer and measurement quality
A large number of quality control measures were built into the survey at the data collection stage and thereafter, to monitor the quality of interviewer performance.
Quality checks were carried out at 10% of productive households. These recalls checked with the participants that interviewers had followed the correct survey procedures when conducting the interview.
In addition to the above quality checking procedure, the computer program used by interviewers had in-built soft checks (which can be suppressed) and hard checks (which cannot be suppressed) associated with particular interview questions. When uncommon or unlikely answers were entered, or answers outside a predetermined range, these checks were triggered and appear as a warning message on the interviewers’ laptop. The interviewer is either encouraged to double-check the entered response (a soft-check) or asked to change it (a hard-check). For example, when young children 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.
Soft-checks were similar to hard-checks, however they could be suppressed. For example, soft-checks were applied to height measurements; if an interviewer entered a respondent’s height to be in excess of 1.93 metres (6 feet 3 inches), a message appeared asking the interviewer to confirm that this entry was correct. The interviewer could suppress the soft-check once they had confirmed that the height entry was not a mistake.
1.5.3 Ethical clearance
Ethical approval for the 2021 survey was obtained from the Health and Care Research Ethics Committee for Wales (REC reference number: 17/WA/0371).
1.6 Survey Response
This section presents the fieldwork outcomes for the sampled addresses. 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) for survey fieldwork were applied across the SHeS, SHS and SCJS. This enables consistent reporting of fieldwork performance and effective comparison of performance between the surveys.
1.6.2 Household response
Tables 1.1a and 1.1b show a detailed breakdown of the SHeS response for sampled addresses in 2021, which are reported separately for the opt-in and knock-to-nudge samples. Addresses with unknown eligibility have been allocated as eligible and ineligible proportional to the levels of eligibility for the remainder of the sample. This approach provides a conservative estimate of the response rate as it estimates a high proportion of eligible cases amongst addresses with unknown eligibility.
At 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 opted-in/consented to interview and was interviewed. The tables show that for the main opt-in sample, 9.7% of eligible households were classed as responding whilst for knock-to-nudge households this proportion was 31.1%. All individual interviews were completed at 7.9% of main opt-in and 22.9% of knock-to-nudge households.
For the child boost sample, 11.8% of eligible households contacted opted in. 3.1% of households that opted in were ineligible as they did not contain any children under the age of 16. For eligible households 87.7% were classed as responding, with all individual interviews complete at 87.5% of households.
Table 1.2a shows that across Heath Boards, the percentage of opt-in households where at least one eligible person was interviewed ranged from 8.3% (Lanarkshire) to 12.1% (Lothian). Fully cooperating households were those where all eligible individuals were interviewed. This varied between 6.0% in the Western Isles to 10.1% in the Borders. The definition of a fully cooperating household changed in 2012 and is therefore not comparable with fully cooperating figures prior to this.
Table 1.2b shows the household response rate for eligible addresses in the opt-in child boost sample by Health Board. This varied from 7.0% (Ayrshire and Arran) to 12.7% (Grampian). Note that the bases for child boost response rates were particularly low in a number of areas (for example 4 eligible households in Dumfries and Galloway and 8 in the Borders).
Table 1.2c shows that across Heath Boards, the percentage of knock-to-nudge households where at least one eligible person was interviewed ranged from 13.3% (Shetland Islands) to 44.7% (Forth Valley). Fully cooperating households were those where all eligible individuals were interviewed. This varied between 16.9% in Ayrshire and Arran to 31.0% in the Highlands. The definition of a fully cooperating household changed in 2012 and is therefore not comparable with fully cooperating figures prior to this
Table 1.3a shows that across Local Authorities, the percentage of opt-in households where at least one eligible person was interviewed ranged from 6.7% (North Lanarkshire) to 14.2% (City of Edinburgh). Fully cooperating households varied between 5.2% (North Lanarkshire) and 11.5% (City of Edinburgh).
Table 1.3b shows the household response rate for eligible addresses in the opt-in child boost sample by Local Authority. This varied from 3.2% (Dumfries and Galloway) to 14.7% (West Lothian). Note that the bases for child boost response rates were particularly low in a number of areas (for example 4 eligible households in Argyll and Bute and Clackmannanshire).
Table 1.3c shows that across Local Authorities, the percentage of knock-to-nudge households where at least one eligible person was interviewed ranged from 12.5% (South Ayrshire) to 61.6% (Stirling). Fully cooperating households varied between 6.8% (South Ayrshire) and 39.7% (Stirling). Tables 1.1a – 1.3c
1.6.3 Individual response for adults
Overall, there were 4,557 adult responses (2,984 from the opt-in sample and 1,573 from knock-to-nudge) to SHeS 2021, as detailed in tables 1.4a and 1.4c.
The adult response rate in 2021 was calculated based on the number of eligible households. This was undertaken by dividing the number of individual adult interviews by the number of eligible adults in productive households. The total estimated number of adults from sampled addresses eligible for interview is referred to as the “set” sample. For 2021, the set sample for adults was 3,429 for the opt-in sample and 1,914 for the knock-to-nudge sample.
Table 1.4a shows the adult response rate broken down by area deprivation for the opt-in sample. The adult response rate ranged from 86.3% in Scottish Index of Multiple Deprivation (SIMD) quintile 1 (most deprived) to 87.8% in quintile 2.
Table 1.4c shows the adult response rate broken down by area deprivation for the knock-to-nudge sample. The adult response rate ranged from 79.8% in (SIMD) quintile 4 to 84.4% in quintile 2.
Table 1.5 shows that the age distribution of respondents to the core opt-in sample was generally older than the population as a whole. For men, 23% of core opt-in respondents were in the 55-64 age group and 22% in the 65-74 age group compared with 17% and 13% of the male population as a whole. There were similar but smaller differences for women, with 21% of female respondents aged 55-64 and a further 21% aged 65-74 compared to 17% and 13% respectively of the female population as a whole. The sex/age profile for the knock-to-nudge sample was closer to the profile of the population as a whole but still with a lower proportion of respondents aged 16-34 and a higher proportion aged 55-74. Tables 1.4a, 1.4c and 1.5
1.6.4 Individual response for children (0-15)
Interviews were undertaken with 1,600 children aged 0 to 15, with 500 interviews taking place as part of the main opt-in sample, 277 as part of the knock-to-nudge sample and 823 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 households that opted-in was used. Tables 1.4a, 14b and 1.4c show that overall response rates for the main sample, knock-to-nudge sample and child boost sample were similar (94.5% for the main sample, 99.9% for the child boost sample and 88.8% for the knock-to-nudge sample).
Tables 1.4a and 1.4c
1.6.5 Intake24 response
A total of 3,447 SHeS adult participants aged 16 and over completed at least one of the dietary recalls, with 3,042 completing both dietary recalls. Similar proportions of men and women completed both of their recalls (86% and 89% respectively). For those who completed any recalls, full completion generally increased with age, with 90% - 91% of those aged 55 and over completing both recalls, with a fairly even spread across the SIMD quintiles (in the range 86% - 89%). Table 1.6
1.7 Weighting The Data
This section presents information on the weighting procedures applied to the survey data. Since 2012 the weighting for SHeS has been 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 of 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.
To undertake the calibration weighting the ReGenesees Package for R was used. 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. There were six steps to calculating the overall adult weights. These were as follows:
1) Address selection weights (w1)
The address selection weights were calculated to compensate for unequal probabilities of selection of addresses in different survey strata, within the opt-in and knock-to-nudge samples. For the main sample there were 32 strata (one for each local authority) for both opt-in and knock-to-nudge.
w0= Number of PAF addresses in the stratum (opt-in/K2N) /Number of addresses selected in the stratum (opt-in/K2N)
To account for the different response rates in the opt-in and knock-to-nudge samples, this was multiplied by the reciprocal of the response rate for opt-in or knock-to-nudge. The address selection weight for each stratum was calculated as:
w1= w0 * 1 /Stratum response rate (opt-in/K2N)
2) Dwelling unit selection weights (w2)
The Multiple Occupancy Indicator (MOI) for the PAF was used to ensure that if there were multiple dwelling units at a single address point then they would have the same selection probability as individual addresses. However, there are likely to have been some cases where the MOI was incorrect. In face-to-face fieldwork, interviewers record where an MOI is different from PAF when visiting a property. This is not possible via the telephone survey, therefore, the information provided
by PAF was assumed to be correct, therefore w2 is effectively 1 for all households.
3) Household selection weights (w3)
Similarly to w2, within a very small number of dwelling units, fieldworkers usually find multiple households, of which only one is selected for participation. Again, due to data collection via the telephone rather than face-to-face, it is not possible to correct for this, therefore w3 was effectively taken as 1 for all households.
4) Calibrated household weights (w4)
The three selection weights were combined (w1*w2*w3) before 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 each SIMD quintile. The population totals that were used were the National Records of Scotland’s (NRS) mid-2020 estimates for private households.
5) 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
- Number of adults in the household
- Employment status of household reference person
- Presence of a smoker in the household
- Marital status
- Urban/rural classification
- Access to a car
- Located within SIMD15 area
- Frequency of eating meals together
Through running backwards and forwards selection procedures for the logistic regression the following variables were included in the final model:
- Health Board
- Number of adults in the household
- Located within SIMD15 area
- Marital status
- Frequency of eating meals together
- Urban/rural classification
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:
w5= 1 /Probability of individual's response
For households of only one adult the non-response weight was one.
6) Individual calibration and final adult weight (int21wt)
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 2020 mid-year population estimates for Health Boards, age/sex distribution at Scotland level and age/sex distribution for the Glasgow and Greater Clyde Health Board.
|Ayrshire & Arran||302,951||60,401||363,352|
|Dumfries & Galloway||123,363||22,982||146,345|
|Greater Glasgow & Clyde||957,186||197,309||1,154,495|
|SIMD Quintile||Total population|
|1 – 20% most deprived data zones||1,044,389|
|5 – 20% least deprived data zones||1,094,217|
1.7.3 Biological module weights
A similar process was applied to derive the weights for the biological module. This is outlined below.
1) Calibrated household weight (w4)
As there was no Health Board boost, the calibrated household weights (w4) were applied from above.
2) Adjustment for biological module selection (bw5)
40% 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:
bw5= PAF addresses in stratum (opt-in/K2N) /Addresses selected in stratum for bio mod (opt-in/K2N) * 1 /w4
3) 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. An additional non-response weight was not required for the biological module as this was carried out as part of the telephone interview.
4) Final calibration for biological module (bio21_wt)
The household (w4), biological sample correction (bw5) and adult non-response (w5) weights were combined (w4*bw5*w5) 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 2020 mid-year population estimates for private households 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, Lanarkshire and Lothian 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. The following steps were followed to derive the weight:
1) Calibrated household weight (w4)
As there was no Health Board boost, the calibrated household weights (w4) were applied from above.
2) 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.
3) Final calibration for Version A weight (verA21wt)
The household (w4) and adult non-response (w5) weights were combined (w4*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 2020 mid-year population estimates for private households 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. The weighting steps are shown below. Steps (1) and (2) followed the same process as described in 1.7.2 above.
1) Address selection weight for main sample and child boost combined (cw1)
2) Dwelling unit (cw2) and household (cw3) selection weights
3) 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:
cw4= Number of children in the household /2
For households with two or fewer children cw4=1.
4) Calibration for child interview weight (cint21wt)
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 2020 mid-year population estimates for private households for Health Boards, age/sex distribution at Scotland level.
Weights were also created specifically for within household analysis, comparing children’s characteristics with those of their parents. As data were only collected with respect to both children and adults in the core sample, these weights were only created for children at core sample addresses. They were created in a similar fashion to that described for the whole of the overall child weights.
1.7.6 Combined weights
A number of different combinations of annual sweeps have been produced to allow the analysis of combined datasets. Due to disruption to the survey at the onset of the pandemic, the survey data collected in 2020 was published as experimental statistics and was not comparable with the time series. This data has not been included in the survey trends or the combined years’ analysis.
|Weight name||Purpose of combined weight|
|int17181921wt||For analysis of 2017, 2018, 2019 and 2021 combined adult data|
|cint17181921wt||For analysis of 2017, 2018, 2019 and 2021 combined child data|
|cmint17181921wt||For analysis of 2017, 2018, 2019 and 2021 combined child data core sample only (for within household analysis)|
|int1921wt||For analysis of 2019 and 2021 combined adult data|
|cint1921wt||For analysis of 2019 and 2021 combined child data|
|bio1921wt||For analysis of 2019 and 2021 combined depression, anxiety, suicide and self-harm data|
|vera1921wt||For analysis of 2019 and 2021 combined version A adult module data|
|cvera1921wt||For analysis of 2019 and 2021 combined version A child module data|
|vera21wt||For analysis of 2021 version A adult module data|
In each case, the calculation of the weights followed the same procedure. The pre-calibration weights which had already been calculated for the individual years (which take into account selection weighting and (except for the child weights) non-response weighting) were combined and calibrated to Health Board and age/sex 2020 population totals for private households.
1.7.7 Intake24 weights
1) Selection and SHeS non-response
The basis for the Intake24 adult weight was the main adult weight (int21wt), which adjusts for the probability of selection and non-response to the survey. This weight was rescaled to a mean of one for all adult respondents eligible for the Intake24 survey.
2) Intake24 non-response weight
Not all of the adults that were invited to take part in the Intake24 survey responded. Using the information collected for the respondent in the main interview and household interview, the likelihood of responding to the Intake24 survey was modelled with logistic regression.
Through running backwards and forwards selection procedures for the logistic regression the following variables were included in the final model for response to the Intake24 survey:
- Health Board
- SIMD Quintile
- Number of adults in the household
- Number of children in the household
- Frequency of eating meals together
- Currently drink alcohol
- Any housework in past 4 weeks
- Gardening/DIY/building work in past 4 weeks
- Whether meets CMO recommendations on activity duration and muscle strengthening
- Whether provide help or care
- Highest qualification held
- Presence of a smoker in the household
The final logistic regression model was then used to estimate the probability of response for all individuals that did respond to the Intake24 survey. The Intake24 non-response weight (intake24_NR) was then calculated as the reciprocal of this probability:
intake24_NR= 1 /Probability of individual's response to Intake24 survey
3) Final calibration of Intake 24 adult weights (intake24_wt)
The adult weight (int21wt) and non-response (intake24_NR) were combined (int21wt * intake24_NR) and applied to the data prior to the final stage of calibration weighting which matched weighted totals for the survey data to the NRS 2020 mid-year population estimates for Health Boards, age/sex distribution at Scotland level and age/sex distribution for the Glasgow and Greater Clyde Health Board.
1.8 data analysis and reporting
SHeS is a cross-sectional survey of the population. It examines associations between health status, personal characteristics and behaviour. However, such associations do not necessarily imply causality. In particular, associations between current health status 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 SHeS 2021 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, 2021 and was interviewed on October 1, 2021 would be classified as being aged 24.75).
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.
Some of the adult data included in the 2021 report have been age-standardised to allow comparisons between groups after adjusting for the effects of any differences in their age distributions. Further information on age standardisation can be found in chapter 2 of this report.
1.8.2 Standard analysis breakdowns
Scottish Index of Multiple Deprivation (SIMD)
The analysis of 2021 data was based on the most recent version of the Scottish Index of Multiple Deprivation (SIMD), published in 2020. 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 (6,976) 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 this report. 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 Design effects and true standard errors
SHeS 2021 used a partially clustered, stratified multi-stage sample design (for the knock-to-nudge element). 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 2021 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 1.10 to 1.19 for selected survey estimates presented in the main report. Tables 1.6a – 1.15b
1.8.4 Intake24 analysis and reporting
Food and portion size codes are automatically assigned within Intake24 allowing the system to generate nutrient output at the individual food level. The raw Intake24 output was imported into a bespoke database to facilitate data checks and to assign foods reported as missing to an appropriate food code and portion size, using the original free text search term and missing food details provided by the participant. Checks were carried out on all the data to identify possible ‘incomplete recalls’. These included recalls with 10 items or fewer (excluding associated foods i.e. milk with tea), recalls that took 2 minutes or less to complete and recalls that contained less than 400kcal. Case by case decisions were made as to whether recalls could be considered valid and complete, including, for example, checking if the respondent said they ate less than usual e.g. sickness. Three participants had one recall that was deemed to be incomplete and these recalls were removed from the dataset.
At the end of the survey data collection, boxplots were generated to review portion sizes and to identify any extreme outliers within each food group. Extreme outliers were identified from the boxplots as individual data points separate from the box and whiskers since they were more than 3 x IQR (Inter-quartile range: 75th percentile-25th percentile) from the nearest quartile for that intake (either the 25th or 75th percentile). These were examined on a case-by-case basis and reviewed in the context of the participant’s overall consumption. Portion sizes which were considered to be implausible, and potentially the result of errors in portion size selection, were adjusted. Adjustments were carried out in the bespoke dietary database by changing the portion code at the individual recall level.
Finally, boxplots were generated to identify any infeasible/extreme energy and nutrient values. As with portions, extreme outliers were looked at on a case-by-case basis. Extreme intakes that were considered to be the result of errors in portion size or food composition were adjusted, otherwise values were left in the dataset as they were assumed to reflect consumption by participants.
The final dietary dataset includes only those respondents who completed two dietary recalls using Intake24, regardless of the day type (i.e. weekdays or weekend days). For each respondent, food and nutrient intake has been calculated based on an average of the two recalls.
Intakes of fruit and vegetables and red meat and processed meats were calculated using disaggregated variables, that is they include these foods eaten as part of composite dishes, as well as their discrete portions, to provide more accurate estimates of total amounts consumed at an individual food level. For example, carrots may be eaten as an accompaniment to a main meal, but they may also be consumed as an ingredient within a stew, together with additional vegetables such as onions and celery.
References and notes
1 The 1995 and 1998 surveys were carried out by the Joint Health Surveys Unit of the National Centre for Social Research (NatCen Social Research) and the Department of Epidemiology and Public Health University College London Medical School (UCL). The MRC Social and Public Health Sciences Unit at the University of Glasgow (MRC SPHSU) joined the consortium in 2003. ScotCen Social Research (a branch of NatCen Social Research), UCL and MRC SPHSU conducted the 2008-2011 surveys after a decision was made to carry out the survey annually.
2 Scottish Surveys Core Questions 2018-2021 Questionnaire Review: Consultation Outcome Report (2017). Available from https://www.gov.scot/publications/scottish-surveys-core-questions-2017/
3 Questionnaire Content of the Scottish Health Survey (2017): Consultation Analysis Report. Available from https://www.gov.scot/publications/questionnaire-content-scottish-health-survey-consultation-analysis-report-april-2017/
4 Dean, L and McLean, J (eds). The Scottish Health Survey 2018 edition: Volume 2: technical report. Edinburgh: Scottish Government Available from: https://www.gov.scot/publications/scottish-health-survey-2018-volume-2-technical-report/
5 Further information on the sample designs and the methodology used is available here: https://www2.gov.scot/Topics/Statistics/About/SurveyDesigns201215.
6 Further information on the 2011 Scottish Health Survey questionnaire review for the 2012-2015 surveys can be found on the Scottish Government SHeS website: https://www2.gov.scot/Topics/Statistics/Browse/Health/scottish-health-survey/questionnairereviewreport
7 Questionnaire Content of the Scottish Health Survey (2017): Consultation Analysis Report. Available from https://consult.gov.scot/population-health/scottish-health-survey/
8 Further information on the 2017 Scottish Health Survey questionnaire review for the 2018-2021 survey can be found on the Scottish Government website: http://www.gov.scot/Resource/0053/00537370.pdf
9 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.
10 Lynn, Peter, Beerten, Roeland, Laiho, Johanna and Martin, Jean ‘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. 2001.
11 A report on the development of the weighting procedures is available here: https://www2.gov.scot/Topics/Statistics/About/Surveys/WeightingProjectReport
12 Scottish Health Survey – telephone survey – August/September 2020: main report. Edinburgh, the Scottish Government. Available from: https://www.gov.scot/publications/scottish-health-survey-telephone-survey-august-september-2020-main-report/
13 Where time series SIMD data are presented, the appropriate version of the SIMD is used for each year. More details are provided within the main report and at https://www.gov.scot/publications/?term=SIMD&cat=filter&publicationTypes=statistics&page=1
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