This cohort comprises 550 individuals, who were tested on cognitive and medical indices on multiple occasions; at first test wave participants were aged ~79 years (Deary et al., 2004b; Houlihan et al., 2010). They were all born in 1921 and most took part at age 11 in the Scottish Mental Survey of 1932. They were Caucasian and almost all lived independently in the Lothian region (Edinburgh city and surrounding area) of Scotland. The data for this analysis was based on the second test occasion, when they were measured on all three relevant speed traits. Genomic DNA was isolated from whole blood from 542 participants by standard procedure at Medical Research Council Technology, Western General Hospital, Edinburgh. Sixteen samples failed quality preceding the genotyping procedure. A reduced sample of 302 individuals had both genotype and phenotype data; their mean age was 83.35 years (SD = .54, range = 82.0–84.6 years) at data collection.
