Cohort Profile Update: The Lothian Birth Cohorts of 1921 and 1936

The original Lothian Birth Cohorts of 1921 (LBC1921) and 1936 (LBC1936) were designed as follow-up studies to the Scottish Mental Surveys of 1932 (SMS1932) and 1947 (SMS1947), respectively. The SMS1932 took place simultaneously across schools in Scotland on 1 June 1932, and used the Moray House Test (No. 12; MHT) of general intelligence. Almost every child attending school and born in 1921 (N 1⁄4 87 498) was tested. The same MHT was administered to almost every child born in 1936 and attending school on 4 June 4 1947 for the SMS1947 (N 1⁄4 70 805). As described in the Cohorts Profile published in 2012, decades later, participants of both Surveys, mostly living in Edinburgh and the surrounding area (the Lothians) in older age, were invited to participate in the Lothian Birth Cohort (LBC) studies. Between 1999 and 2001, 550 of the SMS1932 were recruited to Wave 1 of the LBC1921 study, at a mean age of 79 years. Between 2004 and 2007, 1091 members of SMS1947 were recruited to Wave 1 of the LBC1936 study, at a mean age of 70 years. Both cohorts re-sat the MHT at initial follow-up. In addition, a large amount of other cognitive, psychosocial, lifestyle, medical, biomarker, genetic, brain imaging and other data were collected. There are baseline protocol articles for LBC1921 and LBC1936, and a separate baseline brain imaging protocol article for LBC1936. What is the reason for the new data collection?