home as the need arose. In addition to medical examinations, the men
were given occasional assessments of personality and cognitive abilities.Between 1965 and 1967 about half the participants were given Cattell’sl6PF .
In 1975, we readministered a form of the 16PF to a group of 139
men, originally aged 25–82. Among other things we were interested inseeing if there were systematic declines or increases in the traits mea -
sured by the 16PF . Of the 16 scales, two, intelligence and social inde -
pendence, were significantly higher at the second administration; 14
showed no evidence of change over the 10-year interval studied. Ten -
sion, adventurousness, liberal thinking, tender-mindedness, and super -
ego strength—among other traits—neither increased nor decreased for
the average man in this sample. In retrospect, we view this as the majorfinding of the study . At the time, however, we were as curious as every -
one else about the changes. The scales that absorbed our attention were
the two that changed. But as we examined our findings in detail, it be-came clear that they were probably notthe elusive age changes we had
been seeking.
In 1975 the participants scored higher on measures of intellectual
brightness and social independence. We suspect the increase in intelli-gence scores was probably a matter of testing. When people are giventhe same test twice, they tend to do better the second time, even thoughthey are not actually any more intelligent—this is known as a practice
effect . In addition, the test was given at the laboratory on the first occa-
sion, under timed conditions; in 1975, the men completed the test athome, at their own pace. Allowing more time may have improvedscores. We concluded that it was unlikely that the men had actuallybecome more intelligent with age. (In any case, we do not regard intelli -
gence as a dimension of personality , and we leave it to our colleagues in
cognitive aging to chart the course of mental abilities in adulthood.)
The longitudinal change in the social independence scale was more
puzzling. For one thing, there were no cross-sectional differences in thistrait. That probably meant that, if real longitudinal changes were takingplace, they were not showing up in cross-sectional comparisons becausethey were somehow obscured by generational differences. It is preciselybecause of the possibility of such confusions that researchers turn tolongitudinal designs; when they find evidence of them, however, it isusually an unpleasant surprise. We were faced with the prospect of ex -
plaining not only why individuals became less dependent on the ap -Growth or Decline in Personality 69