One consistent pattern was found when the facets of N, E, and O
were separately analyzed. NEO-PI Activity showed evidence of declinein four of the five analyses. Because another scale measuring this traitalso showed declines in the Douglas and Arenberg (1978) study , and be -
cause peer ratings also showed declines in Activity (Costa & McCrae,
1992b), it seems reasonable to conclude that as people age, there is amaturational decline in the pace and vigor of life. However, here too theeffect is small and does not outweigh other sources of individual differ -
ences. Many 70-year-olds are more active than many 30-year-olds.
As this chapter makes clear, the simple question of “What happens
with age?” is far from easy to answer. In many areas of gerontology , theseparation of cohort, time-of-measurement, and practice effects fromtrue maturational changes may require a lifetime of work. In personal -
ity , the problem is greatly simplified by the nature of the variables stud -
ied. No matter how you view it, the only consistent evidence points to
predominant stability . With age, adults as a group neither increase nordecrease much in any of the traits identified by major personality in-struments.
RECENT DEVELOPMENTS
Small, Slow Changes
Our integrated approach to interpreting age effects is reasonable, but it
might be argued that the data we have applied it to are inadequate. TheNHANES study (Costa, McCrae, et al., 1986) examined thousands ofpeople over a wide age range. By contrast, our longitudinal and cross-sequential studies used much smaller samples and covered a muchmore limited portion of the lifespan; they may have lacked the statisticalpower to spot very small effects reliably . If there were large age effects tobe discovered, our method would have found them, and we can con -
clude with considerable confidence that there are no large effects after
age 30. But science progresses by making ever smaller and more precisemeasurements. If we want to find out about the possibility of small,slow changes, we need longitudinal studies that use very large samplesor very long intervals. Some of both have recently been reported.
Costa, Herbst, McCrae, and Siegler (2000) conducted a longitudi -
nal study of 2,274 University of North Carolina alumni. They were
about 40 years old at first assessment and were reassessed after 6 to 978 PERSONALITY IN ADULTHOOD