Overestimating the Effects of Aging What happens in psychological aging is complex, and we are only beginning to understand it. What is clear, however, is that psychologists have taken too negative a view of the impact of aging on intellectual functioning. One reason for this is that researchers have relied too heavily on crosssectional studies. As we stated in Chapter 1, cross-sectional studies employ the snapshot approach; they test individuals of different ages and compare their performance. Longitudinal studies, in contrast, are more like case histories; they retest the same individuals over a period of years (Holahan, Sears, & Cronbach, 1995). Psychologists such as Baltes and Schaie (1976; Schaie, 1994) have pointed out that crosssectional studies of adult aging do not allow for generational differences in performance on intelligence tests. Because of increasing educational achievement and other social changes, successive generations of Americans perform at progressively higher levels. Hence, the measured intelligence (IQ) of the population is increasing. When individuals who were 50 years old in 1993 are compared with those who were 50 in 1973, the former score higher on almost any kind of cognitive task. But because the people who were 50 years old in 1993 were 30 in 1973,