Introduction to the Scottish Longitudinal Study
The Scottish Longitudinal Study (SLS) is a large-scale linkage study which has been created by using data available from current Scottish administrative and statistical sources. These include Census data, Vital Events data (births, deaths, marriages), National Health Service Central Register (NHSCR) data (migration in or out of Scotland) and NHS data (cancer registrations and hospital admissions). More detail on the list of data included can be found here: http://www.lscs.ac.uk/sls/data.htm.
The SLS is a replica of the England and Wales Longitudinal Study (LS) which has been running successfully for the past 30 years. The LS was designed as a one percent sample of the England and Wales population. It was begun by extracting information on the relevant people captured in the 1971 census. Information for these people was then linked from administrative, vital events and health datasets through time. Unfortunately, although Scotland was originally included in the LS, it pulled out soon after work began due to the small size of the Scottish sample.
The SLS is similar to the LS, but there are some key differences. First, the SLS is a 5.3% representative sample of the Scottish population, rather than a one percent sample, as in the LS. The SLS began with data from the 1991 census, while the LS began with data from the 1971 census. There are a small number of variables that are included in the LS which are not included in the SLS and vice versa. Most notably, hospital admissions data and marriage events can be linked into the SLS - similar data are not included in the LS.
Approximately 274,000 SLS members have been identified from the 1991 census and information for these individuals has been linked from other datasets, including the 2001 census, vital events and health information.
More information about how the dataset was created, how many SLS members have been traced and other background information can be found in SLS Working Paper 1. Detailed information on the sample quality and tracing and linkage rates for the 1991 sample can be found in SLS Working Paper 2.
Researchers in universities in the UK and in other organisations may be eligible to use the SLS if they think these data are useful to them. The buttons on the left hand side provide access to more detailed information about using the SLS.
Background to the SLS
Why was the SLS set up?
Scotland is disadvantaged relative to England in the poverty of its longitudinal databases (i.e. databases that link individuals' characteristics through time, allowing changing circumstances to be investigated) on demographic, socio-economic and health information. The SLS provides a high quality longitudinal research dataset that can be used to provide an insight into the health and social status of the Scottish population and how it changes over time.
This is important because Scotland is disadvantaged in numerous ways. For example, overall mortality rates are higher than the rest of Britain (commonly described as the 'Scottish Effect'); fertility rates are lower than the rest of Britain; population ageing is a significant problem for the future in Scotland; specific causes of death such as lung cancer and heart disease rank among the worst in Europe; and rates of household deprivation are higher than in the rest of Britain. These issues, and the inter-relationships between them, are examples of what can be explored using the SLS.
What can the SLS be used for?
The SLS includes a range of variables covering cultural, demographic, economic, health, housing and social issues. Using the example of health, the potential uses of longitudinal studies such as the SLS are considerable. Because of the inclusion of socio-demographic data from censuses and other sources an added dimension can be brought to the analysis of health variations and inequalities. Social differentials in health and mortality can be explored using such measures as the Registrar General's social class, deprivation indices, NSSEC, occupation and industry, housing tenure, car access, overcrowding and lack of amenities in housing, ethnicity and sex. The effects of geography and migration can also be examined. Change over time can be looked at with reference to a person's later health or their cause of death because of the linkage of data from more than one census. Events such as marriages and migration histories are also included. More information about the datasets that have been linked is available at: http://www.lscs.ac.uk/sls/data.htm. More detailed information on all the variables held in the SLS can be found at: http://www.lscs.ac.uk/sls/dict.htm.
The England and Wales LS, which this dataset is modelled upon, has been used to look at a range of important questions including: occupational mortality, fertility changes, family reconstitution, women's occupations, geographical and social inequalities in health, social mobility, ethnic health etc. Much of the work done using this database in England and Wales has fed into government social policy, particularly into the health targets defined by the Department of Health. For further information about work conducted with the LS see: http://www.celsius.lshtm.ac.uk/publications.html.
How does the SLS compare to other datasets?
Longitudinal studies have a long history in British social and epidemiological research and the majority are based on surveys or panel studies. Some studies, like the British Household Panel Study (BHPS) do use sampling with replacement but most do not. However, all these studies rely on re-interviews of the same persons over time and a high proportion of study members become lost to follow-up. The SLS, like the LS before it, has been set up to collect data that is either required by law (Census, birth registration, death registration, marriage registration) or is a standard administrative function within Britain. As a result, attrition rates are extremely low and linkage rates for events tend to be very high. Also, the sample size is very large compared to most surveys or panel studies.
What about data confidentiality?
The National Records of Scotland (NRS) encourages wide use of the Scottish Longitudinal Study (SLS), but is at the same time strongly committed to the confidentiality of the individuals in the sample. Confidentiality is thus of high importance to the SLS.
SLS records available for analysis are anonymised individual-level data that have not been aggregated or disguised. A range of measures has been taken to ensure confidentiality. The data are held only at the NRS site and they can be accessed only from a secure room using NRS stand-alone computers. Remote data access is not possible. The only aggregated data outputs that can be sent to SLS users are tabulations and model outcomes (such as regression coefficients). Outputs are always sent encrypted. Researchers who need to work with individual-level data may visit the SLS safe setting in Edinburgh to analyse their data. Support officers are available to help users extract and use the data in the correct way. SLS users are instructed thoroughly about the confidentiality rules, and they are required to sign an SLS Undertaking Form describing how they must hold and use any data received from the SLS before they can enter the phase of data analysis.
Use of SLS data is also covered by the National Statistics Code of Practice and, in particular, the Protocol on Data Access and Confidentiality. Specific legislation also covers the release of information held in the SLS: for example, the 1920 Census Act, the 1938 Population (Statistics) Act and the 1984 and 1998 Data Protection Acts and the Freedom of Information Legislation.
More background reading about the SLS governance arrangements can be downloaded from here.
How are the SLS data managed?
The SLS database is designed to provide 'safe data in a safe setting'. Much of the data held is confidential in nature and cannot be used in raw form. The database design has taken this into consideration and the SLS is not a publicly accessible dataset available through any of the academic data archives. It has been constructed as a data repository on a stand-alone network from which data can be accessed by dedicated staff. Further details about how to access the data can be found at: http://www.lscs.ac.uk/sls/access.htm.
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