The Scottish Longitudinal Study A New Source for Scottish Research

1. The Scottish Longitudinal StudyA New Source for Scottish Research Paul Boyle

2. The (Scottish) Longitudinal Study • The England and Wales Longitudinal Study (LS) established following 1971 Census • To study occupational mortality and fertility • Scotland included originally • Withdrew for funding / sample size reasons • Original files destroyed • Re-establishing the SLS • Funded by SHEFC and CSO (£1.5 million) • Working in close collaboration with GRO(S) • Borrowing as much as possible from ONS

3. People • Director: Paul Boyle • Project Manager (Technical): Lin Hattersley • Project Manager (Staff): Katherine Chisholm • Programmer: Zengyi Huang • Programmer: Joan Nolan • 20 form pickers / clerical assistants • Research Fellow (Andy Cullis) • Research Fellow (Vernon Gayle)

4. Management committee • Paul Boyle (University of St Andrews) • Allan Findlay (University of Dundee) • Robin Flowerdew (University of St Andrews) • Sally Macintyre (University of Glasgow) • Steve Platt (University of Edinburgh)

5. Steering committee • David Orr (GROS) • Paul Boyle (SLS) • Ian Mate (GROS) • Muriel Douglas (NHSCR) • Lin Hattersley (SLS) • Rod Muir (ISD, PAC) • Louisa Blackwell (ONS) • Secretary: Katherine Chisholm (SLS)

6. What is the SLS? • Provides linked data from the Scottish Census and administrative records • Sampling based on 20 ‘semi-random’ birthdays • Initial sample drawn from the 1991 Census • Similar sample drawn from 2001 Census

7. Data sources • Vital statistics • Live births • Stillbirths • Infant mortality • Deaths • Widow(er)hoods • Marriages • Health data • Cancer registrations • Census • 1991 Census • 2001 Census • Including data on occupation, economic activity, housing, ethnicity, age, sex, marital status, health, education, religion etc. • Population data • Immigration • Emigration

8. Data sources • Vital statistics • Live births • Stillbirths • Infant mortality • Deaths • Widow(er)hoods • Marriages • Health data • Cancer registrations • Hospital admissions • Census • 1991 Census • 2001 Census • Including data on occupation, economic activity, housing, ethnicity, age, sex, marital status, health, education, religion etc. • Population data • Immigration • Emigration

11. Strengths • Sample size much larger than most surveys • BHPS has ~10,000 people in GB • SLS has ~278,000 members + ~518,000 household members in Scotland (1991) • The census is compulsory • Linkage and trace rates are high • Includes those in communal establishments • Ability to link hospital admissions data to socio-economic characteristics

12. Weaknesses • Restricted range of variables • Smoking • Income • Census information only collected every decade • Not possible to return to the sample to ask extra questions • The data are highly confidential

13. How does the SLS differ from the LS? • Sample percentage larger (5.5% vs 1%) • 20 SLS birthdays, but includes the four LS birthdays • Fewer censuses captured • SLS 1991 & 2001 (currently planned) • LS 1971, 1981, 1991, 2001 • Some variables in the LS not coded in the SLS • e.g. 1991 place of work • Some variables in the SLS not coded in the LS • e.g. hospital admissions and marriages • The SLS is cheaper!

14. How far have we got? • Identification of 1991 sample • Electronic records extracted from 1991 Census • Forms have been ‘picked’ • Flagging data passed to NHSCR • Coding 1991 ‘difficult to code’ information • Only originally coded for 10% Census • Designed interface for data input • Implementing occupation and industry coding software • 62,000 basic coding completed • 5,000 occupation and industry coding completed • Programming derived variables

15. Linkage and ‘flagging’ through NHSCR • 278,359 have been actioned • 241,591 have been flagged • 2,316 of these are new births • 611 are Scottish duplicates • 10,258 have been sent to CR Southport to flag on the English/Welsh database • 12 are English duplicates • 3,268 are dummy records • 22,583 are in the process of being actioned following further patient information • 36 are no trace

16. Vital statistics • Specifications completed • 1991 test data received • 2001 Census information • Commissioned ‘top up’ coding of 65-74 year olds and 10-year occupational coding • Received pre-one number census download, to allow flagging of imputed data • Received post-one number census download, which includes imputed characteristics • Hope to ‘complete’ the job in 2004

17. Potential uses of the SLS • Source data for academic research / social policy / government departments etc. • Analysis of successive census data • The links between social and geographical mobility • The changing geographical distribution of the ageing population • Work patterns of men and women through the lifecourse

18. Analysis of successive event/health data • Studies of changes in birth spacing • Associations between fertility and later diseases • The changing importance of different cancers • Analysis of census and event/health data • Occupational mortality and morbidity • Economic status and diabetes • Socio-economic factors and teenage pregnancy • Marital status differences in self-reported illness • Survival analysis of cancer by area deprivation and occupation • Housing tenure and respiratory disease

19. Why are Scotland’s fertility rates significantly lower than the rates in the rest of Britain? • How do in-migrants fare after arrival in Scotland? • Are older people becoming healthier in Scotland? • Are health inequalities widening between the better and worse off in Scotland? • Given that Scotland has some of the highest lung cancer rates in the world, what are the characteristics of those who succumb to the disease? • Do unemployed people in Scotland ‘get on their bikes’ and move to places where unemployment rates are low, or not?

20. Accessing the SLS • A culture of data sharing • The data will be kept in a ‘secure environment’ • A team will be established to provide access to the data • A ‘data dictionary’ will be released once the dataset is completed • Researchers will not receive individual-level SLS data directly • Data will only be released as tabulations, statistical summaries or aggregated data • In-house ‘safe-setting’ modelling of individual-level data (by support team)

21. Why does Scotland need the SLS? 1991 deprivation in Scotland compared to England & Wales

22. 1991 deprivation census variables in Scotland and England & Wales

23. 1996 age-standardised all cause mortality per 100,000 in Europe

24. 1996 age-standardised mortality for all malignant neoplasms per 100,000 in Europe

25. 1996 age-standardised mortality for malignant neoplasm of the trachea, bronchus and lung per 100,000 in Europe

26. Brief examples of LS research • Does migration exaggerate the relationship between deprivation and self-reported illness? • Cross-sectional studies assume deprivation influences health outcomes • However, people move around • Migration is selective, not random • Health may influence migration • Are the ill more likely to move towards deprived places, and the well to move away from them? Norman P, Boyle PJ and Rees P (forthcoming) Selective migration, health and deprivation: a longitudinal analysis Social Science and Medicine

27. Age distribution of cohorts 1971, 1981 and 1991

28. SIRs 1991

29. SIRs 1991 SIRs 1971

30. Other related activities • Adding local-area geographical data to longitudinal datasets (ESRC) • Ideally small area information would be available • Raises disclosure risk and confidentiality problems • A strategy for adding geographical variables / identifiers which does not cause disclosure problems • Training in longitudinal methods for the social sciences (ESRC) • Collaborative project with the University of Stirling • Integrated programme of training activities • Traditional training and distance learning package

31. The future…? • Linkage of additional data into the SLS • Historical IQ tests? • Benefits data? • Educational data? • New forms of data access • Web-based project design • Teaching package with a single dataset

32. British LS (BLS) • Matching variables • Creation of derived variables • Future funding • We only have resources to create the database • Research and technical support funding will be required • Bid currently being considered by ESRC / MRC / Scottish Executive • Research group will provide longitudinal analysis support