The Scottish Longitudinal StudyA New Source for Scottish Research

Paul Boyle

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

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)

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)

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)

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

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

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

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

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

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!

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

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

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

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

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

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?

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)

1991 deprivation in Scotland compared to England & Wales

Why does Scotland need the SLS?

1991 deprivation census variables in Scotland and England & Wales

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

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

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

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

Age distribution of cohorts 1971, 1981 and 1991

SIRs 1991

SIRs 1991SIRs 1971

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

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

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