The sampling approach for the Inpatient experience survey was designed to meet the needs of each NHS Board and inform local improvement work whilst being able to give a meaningfull comparison across Boards and provide national level results.
A stratified sampling strategy was developed through consultation between the Health and Social Care team within the Scottish Government, analysts with ISD Scotland and representatives of each NHS Board.
Design of sample
Sample strata were agreed with each NHS Board to meet their needs in providing local results at the most useful level. These strata were defined either at site (hospital) level, sub-site (directorate or grouped specialties) level or as groupings of smaller hospitals, depending on what was most appropriate for each NHS Board.
Eligible people were identified from an extract from ISD's Scottish Morbidity Register database ( SMR01) of hospital admissions.
Eligible people were defined as adults (aged 16 years old and above on discharge from hospital) who had an overnight stay in hospital as an inpatient (defined as one night or more where the individual was in hospital at midnight in an inpatient bed) between April 2015 and September 2015.
Details of the type of people excluded from the survey are as follows:
- People who received privately funded care in NHS or private hospitals
- Scottish NHS patients treated in hospitals outside of Scotland but whose care was commissioned by an NHS Board
- People who were not resident in Scotland, with the exception of Northumberland residents treated in NHS Borders
- People who were receiving care as an outpatient or day case which did not result in an overnight stay
- People who were expected to have an overnight stay at admission but did not
- People who stayed in hospital for termination of pregnancy
- People who stayed in a hospital maternity unit
- People who were known to be deceased, i.e. those who had death recorded in SMR01 records
- People treated in a private hospital
- People treated in a hospice
- Inpatients who were being treated for a mental health condition in a mental illness hospital
- Inpatients who were resident in a long-stay hospital
- Inpatients who were being treated in a learning disabilities unit, and
- Inpatients aged 15 or less on discharge
Based on the selection and exclusion criteria, the total number of inpatients who were eligible to take part in the study was 183,363  . Table 3 summarises the total number of eligible inpatients within each NHS Board.
Table 3: Total number of eligible inpatients within each NHS Board including deceased people
|NHS Board||Inpatient Population|
|NHS Ayrshire & Arran||14,731|
|NHS Dumfries & Galloway||4,601|
|NHS Forth Valley||8,374|
|Golden Jubilee Foundation||3,685|
|NHS Greater Glasgow & Clyde||50,686|
|NHS Western Isles||781|
The sample size calculation was based on a 95% confidence level, with a margin of error of 5% either side. This produced results which would be accurate to within +/- 5 percentage points. Where the sample site has less than 1,000 inpatients in the sampling period, this was increased to +/-7 percentage points to avoid sampling too many people.
Table 4 shows that to achieve this level of accuracy, 22,062 completed returns were required.
Expected response rates within each NHS Board were calculated based on the response rates achieved by the 2014 Survey. These were used to adjust the required sample size to allow for non-response.
Table 4 shows that after applying these expected response rates the total sample size was 44,575.
Table 4: Required sample and total selected sample
|NHS Board||Required sample||To allow for non-response||Proportion of inpatients sampled|
|NHS Ayrshire & Arran||2,334||5,104||35%|
|NHS Dumfries & Galloway||982||1,879||41%|
|NHS Forth Valley||530||1,059||13%|
|Golden Jubilee Foundation||636||851||23%|
|NHS Greater Glasgow & Clyde||6,412||13,144||26%|
|NHS Western Isles||225||395||51%|
A list of eligible people was produced by ISD Scotland by combining a list of people extracted from Scottish Morbidity Register database ( SMR01) of hospital admissions and a list provided by NHS Greater Glasgow & Clyde.
The final sample frame was compiled from the list of eligible people after duplications, incomplete records, deceased people and ineligible people were removed.
A random selection of people for each strata was chosen from the final sample frame based on a random number generated on the uniform distribution U(0,N), where N is the total number of people within that sampling strata, with each person selected allocated a unique number.
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