Birth Cohort 1936, and the Norwegian Cognitive NeuroGenetics sample. In each case, the scores on a number of fluid-type cognitive tests were subjected to PCA. The tests used to form the gf factor in the LBC1921 were the Moray House Test, Raven’s Matrices, Logical Memory, and Verbal Fluency. For the LBC1936 the six tests from the WAIS-IIIUK were used. The ABC1936 gf factor included Raven’s Progressive Matrices, Digit Symbol, Uses of Common Objects, and AVLT. For the NCNG sample, a hierarchy of PCA analyses was used (see Supplementary Methods for further details). In all cases a single component was indicated and was extracted. Thus, individuals’ scores on the first unrotated principal component were used as the indicator of general fluid-type intelligence (gf). For gf in the Manchester and Newcastle samples empirical Bayes’s estimates for each individual were obtained from a random effects model fitted by maximum likelihood (ML) to the standardized age-regressed residuals obtained for each sex from the Alice Heim 4 test and the Cattell Culture Fair test scores. All of the phenotypes were corrected for age and sex (with the exception of Manchester and Newcastle gf which was derived separately for males and females) and the standardized residuals
