Inpatient Experience Survey 2018: technical report

4. Sample Design

The sampling approach for the Inpatient Experience Survey was designed to meet the needs of each NHS Board and to inform local improvement work, whilst also being able to give a meaningful comparison across NHS Boards and provide National level results.

A stratified sampling strategy was developed through consultation between the analyst team within the Scottish Government, analysts at ISD Scotland and representatives from NHS Boards.

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 specialities) level or as groupings of smaller hospitals, depending on what was most appropriate for each NHS Board.

Sampling Frame

Sampling for this survey was undertaken by analysts at ISD Scotland.

Eligible people were identified from an extract from ISD's Scottish Morbidity Records 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 2017 and September 2017.

Details of the type of people excluded from the survey are as follows:

• People who received privately funded care in NHS or private hospitals;
• People treated in hospitals outside of Scotland but whose care was commissioned by an NHS Board;
• People who were not resident in Scotland;
• 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;
• Women who stayed in hospital for termination of pregnancy;
• Women who stayed in a hospital maternity unit;
• People who were known to be deceased, i.e. those who had death recorded on SMR01 records and/or the National Records of Scotland Deaths Database;
• People treated in a hospice;
• People who were being treated for a mental health condition in a mental illness hospital;
• People who were resident in a long-stay hospital;
• People who were being treated in a learning disabilities unit;
• People not registered with a GP Practice and;
• People aged 15 or less on discharge from hospital.

Unfortunately, an error which occurred during the sampling process resulted in one strata in NHS Ayrshire and Arran (Medical, Cardiac, Geriatric in Ayr Hospital) also being excluded from the 2018 survey. This affects not only this strata, but also the organisational levels it is associated with: hospital, NHS Board and Region. This omission has been highlighted within the dashboard of local level results and a separate survey is being undertaken in this area to rectify this error. The local level analysis will be updated once that additional survey has been completed.

The addresses from the Community Health Index ( CHI) were cross checked against the Postcode Address File to ensure that they were complete. Any records where the address wasn't recognised were removed from the survey sample frame, as were a small number of people who had requested not to be included in this or other surveys.

Based on the selection and exclusion criteria, the total number of inpatients who were eligible to take part in the survey was 180,713 ^[3] .

Sampling Design and Sample Size Calculation

Sampling was undertaken within strata, to achieve a reasonably reliable result for each strata. The agreed level of reliability was an estimate of a percentage that has a 95 per cent confidence interval with width +/- five percentage points, sampled from a finite population. When the strata had less than 1,000 inpatients in the sampling period, this was increased to a width of +/- seven percentage points to avoid sampling too many people.

The sample size that was calculated for each strata was based on the minimum number of responses required to meet the agreed level of accuracy, adjusted upwards to allow for assumed non-response to the survey. Expected response rates within each NHS Board were calculated based on the response rates achieved in the 2016 Survey.

For strata where the calculated required sample size is greater than the number of eligible inpatients in the sampling period, all eligible inpatients are sampled.

Table 4 shows the Inpatient population, required number of responses and sample sizes at NHS Board level.

Table 4: Sample size by NHS Board