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Chapter 1: Methodology and Response

Jamie Robertson, Scott Jackson & Anna Terje

1.1 Introduction

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 2012-2017 surveys are being conducted by ScotCen Social Research and Medical Research Council Social and Public Health Sciences Unit ( MRC SPHSU) in collaboration with the Centre for Population Health Sciences at the University of Edinburgh and the Public Health Nutrition Research Group at the University of Aberdeen [1] .

1.1.2 Aims of the Scottish Health Survey

The purpose of SHeS is to provide information at the 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 the rest of Britain
  • 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 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 2012-2017 surveys remains 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. Although the number of deaths by IHD has reduced over recent years, it remains one of the most common causes of death in Scotland [2] .

The SHeS series now has trend data going back 21 years; providing the time series is an important function of the survey.

1.1.3 Key changes to the survey methodology in 2012

A number of changes to the survey methodology were introduced following the 2011 Scottish Government review of Scotland's major household surveys. The key changes to SHeS introduced in 2012 for the 2012-2017 surveys were:

  • Sample of addresses drawn by the Scottish Government
  • Inclusion of a set of harmonised core questions asked across the three major Scottish Government household surveys [3]
  • Reduction in the achieved sample size
  • Discontinuation of a module of questions on Knowledge, Attitudes and Motivations ( KAM) to health
  • Introduction of interviewer administered biological samples and measurements to replace the nurse interview

These changes are discussed in greater detail in Volume 2 of the 2012 technical report [4] .

1.1.4 The 2016 survey

The 2016 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 was 0+.

A sample of 9,623 addresses was drawn from the Postcode Address File ( PAF) in 2016. These addresses comprised four sample types: main (core) sample with biological measures, main (core) sample without biological measures, child boost screening sample, and Health Board boost sample. Ayrshire and Arran, Fife and Grampian opted to boost the number of adults (16+) interviewed in their area in 2016. The table below shows the number of addresses drawn for each sample type and the people eligible for interview within each sample type.

The 9, 623 addresses were grouped into 477 interviewer assignments, with around 40 assignments being issued to interviewers each month between January 2016 and December 2016.

Sample type Number of addresses issued in 2016 Eligible for interview
Main (core non-bio) 2,807 Max of 10 adults (age 16+) and 2 children (age 0-15)
Main (core bio) 1,689 Max of 10 adults (age 16)
Child Boost 4,181 Only households containing children aged 0-15 were eligible to participate (up to two children at these households were eligible to be interviewed)
Health Board Boost 946 Adults only (age 16+) (Max of 10)
Total 9,623

Data collection involved a main computer assisted interview ( CAI), a paper self-completion questionnaire, height and weight measurements and, if applicable, adults also completed the biological module. Of the 4,496 main addresses issued, 1,689 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 biological module. Only interviewers that were specially trained in administering biological measures and samples were allocated to work on these addresses.

1.1.5 The 2016 SHeS annual report

The 2016 report consists of two volumes, published as a set as 'The Scottish Health Survey 2016'. 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 SHeS website along with a short summary report of the key findings from the 2016 survey (www.gov.scot/scottishhealthsurvey). Supplementary web tables are also available on the website. These provide a large number of breakdowns by age group, deprivation, income, occupation and long-term condition.

1.1.6 Comparisons with previous surveys in the SHeS series

In the 2016 report comparisons are made with data collected earlier in the series (1998-2015 for children and 2003-2015 for adults). 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.

In addition, this report includes analysis from a number of combined datasets: one for the years 2013 to 2016 combined and one for the years 2015 and 2016 combined to aid analysis of small subsamples of the population; and one for the years 2014 and 2016, for the analysis of questions which are included every second year. Combining data across years in this way allows for a more detailed analysis of subgroups in the sample and of questions with small sample sizes in one survey year – for example number of hours provided by carers and eating habits for adults which are only asked on a biennial basis as part of the Core Version A rotating module. Tables in the report indicate whether the figures presented are based on a single year's data or combined data from across survey years.

1.1.7 Health Board level analysis

Since 2008, the SHeS sample has been designed to be representative of adults at the Health Board level (for all Boards) after four years of data collection have taken place. Analysis of the 2013 to 2016 data by NHS Health Board is published at the same time as this report, and is available on the SHeS website ( www.gov.scot/scottishhealthsurvey). Health Boards with larger samples may be able to analyse data at their Board 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. Going forwards, 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 on data from 2012 to 2015 combined, 2013 to 2016 combined and once it becomes available, also for 2014 to 2017 combined.

1.1.8 Access to SHeS data

Data from the 2016 survey will be deposited at the UK Data Service along with a combined 2013-2016 dataset and a combined 2014/2016 dataset as well as a 2015/2016 dataset. Datasets from earlier years in the series are also deposited here ( www.data-archive.ac.uk).

1.2 Sample Design

1.2.1 Requirements

The sample specification for the 2012-2016 Scottish Health Survey ( SHeS) was designed by the Scottish Government. The design was coordinated with the 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 [5] .

There were three elements to the SHeS sample in 2012-2016:

1) Main adult sample - to allow annual reporting of Scotland level results and results at Health Board level at the end of the 2013- 2016 four year cycle. This required an annual interview target of 4,006 adults for Scotland as a whole and a minimum of 125 for each Health Board. 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 1,785 child interviews for Scotland. As the main sample was only expected to yield 780 child interviews, a further 1,005 interviews were required from a separate boost sample.

3) Health Board boosts in 2016, Ayrshire and Arran, Fife, and Grampian Health Boards commissioned boosts to increase the number of adult interviews in their Board area. Each of the Health Boards specified a target of 300 additional interviews for their boost.

1.2.2 Sample design and assumptions

For all three elements a 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. This means that over four years of fieldwork all IGs are included in the sample and the combined 2013- 2016 sample will be unclustered. In Orkney, Shetland and Na h- Eileanan Siar the sample was clustered by datazone.

1.2.3 Main sample

As stated above, the annual sample size for Scotland was 4,006 adults with a minimum Health Board sample size of 125 adults. These sample sizes were the minimum required to allow effective reporting of Scotland-level results annually and Health Board results at the end of the four year 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, 2012-2016, 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 level, to allow for coordination with the sample selection of the SHS and SCJS, the sample design was implemented using Local Authorities as strata. This was done by allocating the target Health Board samples to Local Authorities proportionate to population.

Prior to April 2014, there was a slight complication in the design due to Local Authority boundaries not being concurrent with Health Board boundaries. Further information on this can be found in section 1.2.3 of the 2015 Technical Report.

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 for Greater Glasgow and Clyde there would be 1.5 interviews per co-operating household, with 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) As the sample was stratified by Local Authorities, the response rates from the previous surveys were examined. It was found that sample sizes for individual authorities were too small to base response assumptions on. It was also found that it would be inappropriate to base assumptions on Health Boards as there was a high degree of variability for Local Authorities within the same Health Board. 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 for 2016 were then based on the weighted average of responses for 2013, 2014 and 2015. Figure 1B below shows the Local Authority groupings.

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 2009/2010.

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 Na h-Eileanan Siar, 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 2016.

1.2.4 Child boost sample

For the 2012-2016 surveys, 1,785 child interviews were required each year. 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 1,005 interviews.

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

1) The overall target sample of 1,785 child interviews was allocated proportionally to Health Boards based on the child (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 1,785. The following table shows the target sample sizes for the main sample and child boost sample by Health Board.

Figure 1C: Target annual child interviews, 2012-2016, by 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 1,005 1,785

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 sample in the 2008 and 2009 surveys.

3) To estimate the proportion of child-less households data from the 2007-2008 Scottish Household Survey 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, for each Local Authority area, the estimated response rates for the child boost sample were set at 6% higher than the main sample response rate.

5) 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 selected for the child boost sample are shown in Figure 1E.

1.2.5 Health Board boost samples

Each year individual Health Boards are given the opportunity to fund a boost sample to enable them to boost the number of adult interviews in their Board area. For the 2016 survey, Ayrshire and Arran, Fife and Grampian opted to boost the main sample in their areas. The following table shows the target sample size for each of the boosts.

Figure 1D: Target sample for Health Board boosts in 2016

Health Board Target interviews for boost
Ayrshire and Arran 300
Fife 260
Grampian 300
Total 860

As the main sample was selected before boost areas were confirmed, boost samples were supplementary to the main sample. For Ayrshire and Arran 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. For the boost samples, and for samples drawn to addresses shortfalls over the four year period, the same active PSUs as the main sample were used.

Figure 1E: Selected addresses by strata in 2016

Sample strata Main sample Health Board boost Child Boost Total sample
Aberdeen City 189 150 173 512
Aberdeenshire 171 135 203 509
Angus 71 - 77 148
Argyll & Bute 74 - 70 144
Clackmannanshire 36 - 44 80
Dumfries & Galloway 129 - 93 222
Dundee City 96 - 95 191
East Ayrshire 83 102 91 276
East Dunbartonshire 81 - 84 165
East Lothian 74 - 86 160
East Renfrewshire 69 - 80 149
Edinburgh, City of 432 - 366 798
Eilean Siar 133 - - 133
Falkirk 108 - 128 236
Fife 262 302 291 855
Glasgow City 538 - 493 1031
Highland 168 - 179 347
Inverclyde 67 - 67 134
Midlothian 61 - 70 131
Moray 65 52 70 187
North Ayrshire 96 112 107 315
North Lanarkshire East 247 - 311 558
North Lanarkshire West 17 - 19 36
Orkney Islands 125 - - 125
Perth & Kinross 99 - 101 200
Renfrewshire 138 - 141 279
Scottish Borders 145 - 61 206
Shetland Islands 122 - - 122
South Ayrshire 80 93 79 252
South Lanarkshire East 207 - 244 451
South Lanarkshire West 49 - 50 99
Stirling 65 - 76 141
West Dunbartonshire 73 - 75 148
West Lothian 126 - 157 283
Total 4496 946 4181 9623

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 can be used to inform assumptions for 2015 sample design
  • It has excellent coverage of addresses in Scotland
  • The small user version excludes the majority of businesses

The Assessor's Portal, 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 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 4 years.

The sample design specified in Section 1.2 was implemented in three stages:

1) All primary sampling units (datazones on the islands, intermediate geographies elsewhere) were randomly allocated to one of the four years of fieldwork. This meant that the sample was drawn from one quarter of PSUs each year and ensured that over four years (2013 to 2016) of fieldwork all addresses had a non-zero probability of selection. One quarter of target adult sample was 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 PSUs were allocated to the biological module and all selected addresses within those PSUs were eligible for the biological interview. 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 PSUs (37.6% in 2016) were allocated to the biological module.

Figure 1F: Primary sampling units selected in 2016

Health Board PSUs in 2016 Sample Total PSUs
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 62 273
Highland 20 76
Lanarkshire 40 137
Lothian 45 177
Orkney 6 27
Shetland 7 30
Tayside 23 90
Western Isles 9 36
Total 326 1,307

2) The required numbers of addresses for the main sample and child boost sample were combined to give an overall total of addresses to sample for each stratum (local authorities plus Lanarkshires split). The overall 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, 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 Postcode Address File ( 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 both the main and Health Board boost samples all adults aged 16 and over in responding households were selected for interview. To ease respondent burden, for child interviews for both the main sample and the child boost sample 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

1.3.1 Introduction

Topics covered in the 2012 to 2017 surveys were agreed following a consultation carried out in 2011 [6] . Many of the topics and questions included in earlier years of the survey were included again, to continue time series. The 2016 survey included the same topics as the 2014 and 2012 surveys, though a small number of new questions were added see (section 1.3.3). As with previous years, the survey had a focus on cardio-vascular disease ( CVD) and its associated risk factors.

A public consultation about the content of the survey from 2018 began in September 2016, with a deadline for responses of Monday 17th October 2016. The consultation analysis report is available from http://www.gov.scot/Publications/2017/04/6455. Decisions about the content of the survey from 2018 will be made and published online in due course.

1.3.2 Documentation

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 included in Appendix A. Protocols for taking measurements (height, weight, waist and blood pressure) and collecting biological samples (saliva and urine) are available on request from ScotCen. 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. The table that follows 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 after the topic name.

Version A households accounted for 62% 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 2016, the topics included in the Version A rotating module were: respiratory symptoms, additional asthma questions, additional physical activity questions and questions about eating habits included for adults (children are asked these questions every year).

Version B households accounted for the remaining 38% of the main (core) sample. At these addresses participants were only asked the core questions during the main interview with participating adults (aged 16+) also eligible to complete the biological module.

Figure 1G: Content of the 2016 Interview

CORE SAMPLE – Main interview outline
Version A Version B
Household questionnaire including household composition
General health (0+) including caring (4+)
Respiratory symptoms 16+ -
General CVD (16+)
Use of health services (0+)
Asthma (0+)
Asthma additional 16+ -
Physical activity adults (16+) and children (2-15)
Sedentary activity adults (16+) and children (2-15)
Additional physical activity questions 2+ -
Eating habits adults 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 significant number of changes were made to the questionnaire content in advance of the 2012 survey based on the 2011 consultation. These changes are discussed in the 2012 Technical Report4 and the SHeS Questionnaire Review Report 2012-20156.

In addition, a small number of questions were introduced to the questionnaire in 2016.

Additional questions on the use of e-cigarettes and vaping devices were added, including questions about frequency of use, age started using e- cigarettes and length of time using e-cigarettes:

The full question wording of all the questions can be found in Appendix A.

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 being asked as part 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 than 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 including parents may be present).

Paper questionnaire booklets were administered for the following groups in the 2016 survey:

Adults - AUDIT questionnaire (designed to identify signs of hazardous or harmful drinking or possible alcohol dependence), General Health Questionnaire ( GHQ12), Warwick Edinburgh Mental Well-being scale ( WEMWBS), gambling, use of contraception, knowledge of the physical activity recommendations, sexual orientation, and cosmetic procedures

Young adults - Smoking (including use of e-cigarettes), drinking, AUDIT questionnaire, GHQ12, WEMWBS, gambling, use of contraception, knowledge of physical activity recommendations, and sexual orientation

13-15 year olds - GHQ12, WEMWBS, and knowledge of the physical activity recommendations

Parents of 4-12 - Strengths and Difficulties questionnaire ( SDQ) year olds designed to detect behavioural, emotional and relationship difficulties in children and knowledge of the physical activity recommendations.

1.3.5 Height and weight

Interviewers measured the height and weight of all participants aged 2 and over, with their consent. Protocols for taking height and weight measures are available on request from ScotCen.

1.3.6 Biological module

As highlighted previously, at a sub-sample (of around 38%) of main core sample addresses, adults (aged 16 and over) were eligible to complete the biological module. Since 2012, specially trained interviewers have been collecting some of the measurements and samples which were collected by nurses prior to this date.

Since the same interviewer administered the main interview and the biological module, the latter could either be completed either immediately after the main interview or on a separate occasion.

As part of the module, 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 blood pressure and waist circumference measurements from participants taking part in the biological module. 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).

Participants were also asked a set of questions about depression, anxiety, suicide attempts and self-harm (taken from the Adult Psychiatric Morbidity Survey) in computer assisted self-interviewing ( CASI) format.

Figure 1H: Content of the 2016 Biological Module

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

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 2016; one for the core version A, additional sample and Health Board boost addresses, one for the core version B (with the biological module) addresses, and a separate version was sent to 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.

In 2016 both the advance letters and survey leaflets were amended to include more details on how personal data are handled by the survey team. Copies of the letters and leaflet are included in Appendix A.

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 randomly selected for interview. Interviewers obtained the verbal consent of both the parent / guardian and the child before commencing the interview. At additional sample and Health Board boost sample households interviewers attempted to interview a maximum of ten adults at selected households. Children were not eligible for interview at Health Board boost addresses or additional sample addresses.

1.4.3 Collecting data

Interviewers used computer assisted interviewing ( CAI).

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 [7] 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 or not they were eligible to take part in the interview. The CAPI program then created individual questionnaires for each eligible participant in the household.

Where possible an individual interview was then carried out with all eligible 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 in a single 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, providing information on the measurements and samples being taken.

A separate version of this leaflet was used for children in 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.

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 in Version B addresses were given a Measurement Record Card which included additional information about the measurements and samples collected in the biological module. Wherever possible, interviewers would complete the module directly after the main interview to minimise attrition. If this was not possible then the interviewer would arrange to go back at a convenient time to complete the module. The module included the measurements described in Section 1.3.6. Written consent was obtained from participants before saliva and urine samples were taken. The consent statements are included in Appendix A.

1.4.5 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 in the home throughout the interview. Information about younger children (aged 0-12) 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 measurement record card.

Participants eligible for the biological module were given the Measurement Record Card for reference. If participants had their waist measurement and blood pressure taken then interviewers recorded their results on this card (if the participant wished).

Interviewers were issued with a set of guidelines to follow when commenting on participants' blood pressure readings. 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 for the child boost sample. They were also trained and accredited in measuring height and weight.

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.

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.

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 initial biological module visit. They are also supervised in the field annually by an experienced survey nurse to ensure they are administering the measurements and samples in line with SHeS protocols. Interviewers are reaccredited annually by the research team and survey nurses.

Full sets of written instructions, covering both survey procedures and measurement protocols, were provided to interviewers (protocols are available on request from ScotCen).

1.5.2 Checking interviewer and measurement quality

A large number of quality control measures were built into the survey to check on the quality of interviewer performance at both the data collection stage and subsequently. 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 entered which fell outside a pre-determined 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, some checks were age specific. Some 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 child. 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 2016 survey was obtained from the Health and Care Research Ethics Committee for Wales ( REC reference number: 12/WA/0261).

1.6 Survey Response

1.6.1 Introduction

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) [8] for survey fieldwork were applied across the SHeS, SHS and SCJS. This enables consistent reporting of fieldwork performance and effective comparison between the performance of the surveys.

1.6.2 Household response

Table 1.1 shows a detailed breakdown of the SHeS response for all sampled addresses for Scotland in 2016. 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 was interviewed. The table shows that for the combined main, additional sample and Health Board boost sample, 57.6% of eligible households were classed as responding, and with all individual interviews complete at 46.6% of households.

For the child boost sample around three-quarters of households were ineligible as they did not contain any children under the age of 16. For eligible households 64.8% were classed as responding, with all interviews complete at 64.7% of households.

Table 1.2 shows that across Heath Boards the household response rate ranges from 49% (Lothian) to 70% (Orkney Islands). Fully cooperating households were those where all eligible individuals were interviewed, all height and weight measured and, if eligible, completed the biological module. The definition of a fully cooperating household changed in 2012 and is therefore not comparable with fully cooperating figures prior to this.

Table 1.3 shows that the household response rate for eligible addresses in the child boost sample varied from 50% (Borders, albeit based on a sample of just 10 eligible addresses – next lowest area being Tayside at 53%) to 84% (Highland). Tables 1.1- 1.3

1.6.3 Individual response for adults

Overall there were 4,323 adult responses to the 2016 SHeS with 968 responses to the biological module, detailed in Table 1.4.

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 households. This was undertaken by calculating the average number of men and women per household for responding households and non-responding households (where information on the composition is known) and applying this to the households where nothing is known. The total estimated number of adults from sampled addresses eligible for interview is referred to as the "set" sample. For 2016 the set sample of men was 3,973 and for women 4,462.

Table 1.4 shows the adult response rate broken down by gender. The adult response rate was 48% for men, 54% for women and 51% overall. In responding households (those households where at least one interview was completed) additional information on respondents allowed the consideration of response to stages of the survey by gender and age group. This is shown in Tables 1.5 and 1.6. For both men and women the younger age groups were found to have a lower response rate (67% for men aged 16 to 24 and 74% for women aged 16 to 24) than older age groups (91% or higher response rate for men over 65 and for women over 25).

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, and provided a saliva sample, but there was a drop off in providing the urine sample. Of those eligible for the biological module (including non-responders to the main interview in participating households), 60% of men participated in the module (57% provided waist measurements, 56% blood pressure measurements, 54% a saliva sample, and 50% a urine sample), as did 69% of women (65% with waist measurements, 63% blood pressure, 63% saliva, and 56% urine).

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. Tables 1.4- 1.6, Table 1.9

1.6.4 Individual response for children (0-15)

Interviews were undertaken with 1,561 children aged 0 to 15, with 757 interviews taking place as part of the main sample and 804 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 the main sample and child boost sample were similar for boys and girls (57-58% in the main sample and 64% for both in 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 98% or higher for every group, however, the response rate for children aged 11 to 15 was slightly lower at 93% for boys and 92% for girls. Table 1.7, Table 1.8

1.7 Weighting The Data

1.7.1 Introduction

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 [9] .

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:

1) 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 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:

Mathematical Equation

2) 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 then 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:

Mathematical Equation

With w2 trimmed to a maximum of 3.

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 SHeS. The following correction was applied for multiple households:

Mathematical Equation

With w3 trimmed to a maximum of 3.

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 SIMD15 areas. The population totals that were used were the National Records of Scotland's ( NRS) mid-2015 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
  • Age / sex
  • Number of adults in the household
  • Employment status of household reference person
  • Presence of a smoker in the household
  • Marital status
  • Tenure
  • 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
  • Age / sex
  • Number of adults in the household
  • Presence of a smoker in the household
  • Marital status
  • Tenure
  • Access to a car
  • Located within SIMD15 area
  • Frequency of eating meals together

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:

Mathematical Equation

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

6) Individual calibration and final adult weight (int16wt)

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 2015 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.

Figure 1I: 2015 Mid-year population estimates for private households in Scotland by Health Board

Health Board Children Adults Total
Ayrshire & Arran 62,085 304,281 366,366
Borders 18,930 93,946 112,876
Dumfries & Galloway 23,620 124,131 147,751
Fife 63,960 296,401 360,361
Forth Valley 52,604 242,652 295,256
Grampian 98,925 475,170 574,095
Greater Glasgow & Clyde 192,727 935,388 1,128,115
Highland 52,891 260,538 313,429
Lanarkshire 118,105 530,650 648,755
Lothian 146,159 700,130 846,289
Orkney 3,422 17,977 21,399
Shetland 4,187 18,778 22,965
Tayside 67,613 335,539 403,152
Western Isles 4,339 22,390 26,729
Total 909,567 4,357,971 5,267,538

Total figures might not be exact due to rounding

Figure 1J: 2015 Mid-year population estimates for private households in Scotland by SIMD15 indicator

SIMD15 Total population
15% most deprived datazones 914,981
All other datazones 4,352,557
Total 5,267,538

Total figures might not be exact due to rounding

Figure 1K: 2015 Mid-year population estimates for private households in Scotland by age group

Age group Male Female Total
0-4 148,745 141,568 290,313
5-9 148,357 143,136 291,493
10-15 167,685 160,076 327,761
16-24 290,881 285,484 576,365
25-34 340,994 356,701 697,695
35-44 322,838 340,841 663,679
45-54 385,532 410,734 796,266
55-64 328,975 346,912 675,887
65-74 256,808 283,587 540,395
75+ 168,129 239,555 407,684
Total 2,558,944 2,708,594 5,267,538

1.7.3 Biological module weights

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

1) 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.

2) Dwelling unit (w2) and household selection weights (w3)

The dwelling unit and household selection weights from the main adult weight were applied as above.

3) 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.

4) Adjustment for biological module selection (bw5)

35.8% 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:

Mathematical Equation

5) 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.

6) 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
  • Any housework in past 4 weeks
  • Economic activity (working / retired / sick)
  • 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

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
  • Marital status
  • Urban / rural classification
  • Located within SIMD15 area
  • Current smoker
  • Currently drink alcohol

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:

Mathematical Equation

7) Final calibration for biological module (bio16_wt)

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 2015 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, Highland, and Lanarkshire were grouped together. For the age groups, the lowest two age groups were combined as were the highest two age groups.

Weights were also created specifically for use with data resulting from the urine samples due to the higher level of non-response to this element of the biological module. These were created in a similar fashion to that described for the whole of the biological module.

1.7.5 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:

1) Address selection weight (bw1)

As derived in the first step of the biological module weight.

2) Dwelling unit (w2) and household selection weights (w3)

The dwelling unit and household selection weights from the main adult weight were applied as above.

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

4) 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.

5) Final calibration for Version A weight (verA16wt)

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 2015 mid-year population estimates for private households for Health Boards, age / sex distribution at Scotland level.

1.7.6 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 97%. The weighting steps are shown below. Steps

(1) and (2) followed the same process as described in 3.2 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:

Mathematical Equation

For households with two or fewer children cw4=1.

4) Calibration for child interview weight (cint16wt)

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 2015 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.

1.7.7 Combined weights

A number of different combinations of annual sweeps have been produced to allow the analysis of combined datasets.

The weights provided for combined years of data are:

Weight name Purpose of combined weight
int13141516wt For analysis of 2013, 2014, 2015 and 2016 combined adult data
cint13141516wt For analysis of 2013, 2014, 2015 and 2016 combined child data
cmint13141516wt For analysis of 2013, 2014, 2015 and 2016 combined child data core sample only (for within household analysis)
bio13141516wt For analysis of 2013, 2014, 2015 and 2016 combined biological data (not urine)
uri13141516wt For analysis of 2013, 2014, 2015 and 2016 combined urine data
int1516wt For analysis of 2015 and 2016 combined adult data
cint1516wt For analysis of 2015 and 2016 combined child data
cmint1516wt For analysis of 2015 and 2016 combined child data core sample only (for within household analysis)
bio1516wt For analysis of 2015 and 2016 combined biological data (not urine)
uri1516wt For analysis of 2015 and 2016 combined urine data
int1416wt For analysis of 2014 and 2016 combined adult data
vera1416wt For analysis of 2014 and 2016 combined version A adult module data
cvera1416wt For analysis of 2014 and 2016 combined version A child 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 2015 population totals for private households.

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 the 2016 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 2016 and was interviewed on October 1 2016 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.

Age standardisation

Some of the adult data included in the 2016 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 have 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 most 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 2015 household population estimates for Scotland. 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:

Mathematical Equation

Therefore p′ can be viewed as a weighted mean of p i using the weights N i. 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:

Mathematical Equation

1.8.2 Standard analysis breakdowns

Scottish Index of Multiple Deprivation ( SIMD)

The analysis of 2016 data was based on the 2016 version of the Scottish Index of Multiple Deprivation [10] . 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 (6,977) 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 2016 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 2016 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 1.10 - 1.19


Contact

Email: Julie Landsberg Julie Landsberg

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