overestimating the Effects of Aging What happens in psychological aging is complex, and w are only beginning to understand it. What is clear, how ever, is that psychologists have taken too negative a vie of the impact of aging on intellectual functioning. On reason for this is that researchers have relied too heavil on cross-sectional studies. As we stated in Chapter cross-sectional studies employ the snapshot approach they test individuals of different ages and compare the performance. Longitudinal studies, in contrast, are mor like case histories; they retest the same individuals over period of years (Holahan, Sears, & Cronbach, 1995). Psychologists such as Baltes and Schaie (197 Schaie, 1994) have pointed out that cross-section studies of adult aging do not allow for generational dif ferences in performance on intelligence tests. Becaus of increasing educational achievement and other soci changes, successive generations of Americans perform at progressively higher levels. Hence, the measure intelligence (IQ) of the population is increasing. Whe individuals who were 50 years old in 1993 are compare with those who were 50 in 1973, the former score highe on almost any kind of cognitive task. But because th people who were 50 years old in 1993 were 30 in 1973