The major appeal of the longitudinal design is its ability to separate
changes from generational effects. People only live once. In their youththey may absorb the characteristic tone of their generation, but havingdone so, they retain it for life. Longitudinal changes cannot be the directresult of generational differences, nor is there much evidence to suggestthat individuals of different generations change in different ways or atdifferent rates, at least with regard to personality .
In contrast to the hundreds of cross-sectional studies, there are
only a relative handful of longitudinal studies of adult personality .The reasons should be clear: It is extremely difficult to keep track ofpeople over a period of many years, and the rewards of longitudinalresearch are remote. In fact, virtually all the studies to be reporteddemonstrate the altruism of a set of foresighted scientists who beganthe measurement of personality in studies others would eventually re -
port.
These studies vary considerably in the kinds of individuals studied,
the methods and instruments used to measure personality , and the in-tervals at which measurements were made. They are quite consistent,however, in their conclusions: There is little evidence of substantial lon-gitudinal change in personality characteristics in the period of adult-hood, from 30 to 80 years of age. Let us turn to some of the specifics.We will review longitudinal analyses of the l6PF because the results aretypical and because the existence of two independent studies makes in-formative comparisons possible. Later in this chapter we return to morerecent studies.
Stability in the 16PF
Our early research on aging and personality was conducted in conjunc -
tion with a longitudinal program sponsored by the Veterans Adminis -
tration (VA) in Boston, the Normative Aging Study (Costa & McCrae,
1978). The participants in this project were 2,000 male veterans, rang -
ing in age from 25 to 90 years. Most were White and long-term
residents of the Boston area. Although there were relatively few individ -
uals from the lowest socioeconomic levels, there was a reasonable repre -
sentation of subjects with a high school education and beyond. Of
course, as in all such studies, the participants were volunteers; in thiscase they had volunteered to return to the VA Outpatient Clinic every 5years for tests. They also completed questionnaires mailed to them at68 PERSONALITY IN ADULTHOOD