The Lothian Birth Cohort 1936 study will examine, among other factors, genetic contributions to individual differences in normal cognitive ageing [27,28]. Additive genetic influences contribute well over half of the variance to cognitive ability in adult humans, including in old age [29-33]. There is evidence of a genetic contribution to cognitive change within old age [34,35], but most studies suffer from a poor phenotype, with cognitive change being assessed across a small period of time.
