For each of the cohorts we constructed cognitive phenotypes of fluid-type and crystallized-type intelligence. Crystallized-type intelligence is typically assessed using tests of acquired knowledge, and most often through tests of vocabulary. Fluid-type intelligence tends to involve unfamiliar, sometimes abstract, materials, to involve on-the-spot thinking, to be completed under time pressure, and to rely relatively little on prior knowledge. Here, to represent crystallized intelligence (gc), we used: the National Adult Reading Test in the Lothian Birth Cohorts of 1921 and 1936, and the Aberdeen Birth Cohort 1936; the Mill Hill Vocabulary Test in the Manchester and Newcastle samples; and the Wechsler Adult Intelligence Scale Vocabulary subtest in the Norwegian Cognitive NeuroGenetics sample. For fluid-type intelligence, principal components analyses (PCA) were used in the following cohorts to derive a general intelligence factor (gf): the Lothian Birth Cohorts 1921 and 1936, the Aberdeen 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
