Disparate time spans in sequential studies of aging.
In several published studies of intelligence and adult age, a sequential design was used in which birth cohort and time of measurement were the independent variables in an ANOVA. The time span of these two variables were quite disparate; the cohort variable covered about 50 years whereas the time-of-measurement variable covered 7 or 14 years. It was demonstrated here that when time spans are disparate, even when all differences are attributable entirely to age changes, the F values typically will be larger for the cohort variable and errors in interpretations became likely. When cohort differences are statistically significant and time-of-measurement differences are not, the conclusion that age differences are "generational" and not due to age changes within individuals may be wrong.
D000328:Adult; D000368:Aged; D000375:Aging; D000704:Analysis of Variance; D006801:Humans; D007360:Intelligence; D008875:Middle Aged; D012107:Research Design / Q000592:standards*; D013997:Time Factors