COHORT PROFILE Cohort Profile: The Scottish Longitudinal Study (SLS)

This article describes the establishment of the Scottish Longitudinal Study (SLS). The study is similar in design to the Office for National Statistics (ONS) Longitudinal Study (LS), which has been running for over 30 years and the Northern Ireland Longitudinal Study (NILS), which has been established only recently. However, the SLS differs from the LS and NILS is a number of ways. Subsequently, we describe the details of the SLS, paying particularly attention to how it compares with the LS upon which is was originally based. In 1974 the LS, which is a continuous, multi-cohort study, was established in England and Wales by the then Office for Population, Censuses and Surveys (OPCS). Those with one of four semi-randomly selected birthdates were extracted from the 1971 Census, providing a 1% sample of around 500 000 individuals. The study has progressed to include census data for four decades (1971, 1981, 1991, 2001), vital events information (births, deaths) and cancer registry notifications. It is now managed and funded by the ONS and the Economic and Social Research Council (ESRC) provide further funding for an academic support service. Although a similar sample was extracted from Scottish 1971 Census data, the 1% sample (around 50 000 people) was argued to be too small to allow research on many of the epidemiological and sociodemographic questions of importance to Scotland. The original Scottish study was, therefore, discontinued in 1981 and, sadly, the original data from the 1970s were not retained. When we revisited the idea of establishing a SLS in the early 2000s, various factors made it feasible. The growing awareness of the value of longitudinal data to answer a range of complex research questions among a number of academic and government researchers led to valuable support for the funding requests. Improvements in computing power, data linkage techniques and the quality of electronically held administrative datasets since the 1970s also meant that embarking on such a linkage study was more technically feasible. On the other hand, attempting to locate and transcribe information from some of the historic census and vital events records raised a series of challenges. A group of academics requested funding from the then Scottish Higher Education Funding Council (SHEFC), now the Scottish Funding Council (SFC), to establish the Longitudinal Studies Centre— Scotland (LSCS), which is responsible for the establishment, maintenance and support of the SLS. Because of the problems associated with the 1% sample size, identified when the Scottish component of the LS was abandoned, this funding allowed for a 2% nationally representative sample, based on eight birthdates (four of these matched those used in the England and Wales LS to allow future comparative studies). Further funding to establish the study was then secured from the Scottish Chief Scientist’s Office (CSO), which allowed us to increase the sample to 5.5%, based on 20 birthdates. Additional funding from the Scottish Executive and, more recently, from the ESRC has since enabled the establishment of the SLS support team that provides tailored, free support to academic researchers wishing to use the dataset.