Individual differences in trajectory of intellectual development over 45 years of adulthood.

The hypothesis that individual differences in adult intellectual development reflect variation in life context and personality was examined in 132 World War II (WWII) veterans. Intelligence data from the Canadian Army M Test were available for 3 occasions, WWII, 1984-1986 (Int85), and 1989-1991 (Int90). Performance declined over the 45 years on 5 subtests but improved on the 6th, Vocabulary. Correlations between WWII and Int90 scores showed considerable stability of individual differences in intelligence over 45 years. Younger age predicted less decline over 45 years on all subtests; a more engaged lifestyle predicted less decline on most subtests, and better health and greater introversion predicted less decline on some subtests. Predictors of change since Int85 were similar to those for the whole period. Implications for theories of adult intellectual development are discussed.