The Lothian Birth Cohorts of 1921 and 1936 are follow-up studies of the Scottish Mental Surveys of 1932 and 1947. The surveys had, respectively, tested the intelligence of almost every child born in 1921 or 1936 and attending school in Scotland in those years. Therefore, tracing and re-testing people who had taken part in the Surveys much later in their lives offered a rare opportunity to examine the distribution and causes of cognitive ageing across most of the life course. The studies were initially set up to study the determinants of non-pathological cognitive ageing, rather than focussing principally on dementia or other pathological cognitive disorders. This page provides information about the Lothian Birth Cohort 1921.