FIGURE 12.4 Age Differences in Intellectual Abilities Cross-sectional data on intellectual abilities at various ages show much steeper declines. Longitudinal research, in contrast, shows more notable rises. Because Schaie’s research is cross-sequential, the trajectories it depicts are more revealing: None of the average scores for the five abilities at any age is above 55 or below 35. Because the methodology takes into account the cohort and historical effects, the age-related differences from ages 25 to 60 are very small.

Source: Schaie, 2005, p. 116.