tive review of the literature) conducted by Roberts and DelVecchio
(2000). Small changes accumulate here and there over time, and the netresults is a slow decay of initial rank ordering. Based on GZTS data, weprojected that about 60% of the variance in personality trait scores ispreserved over the full adult lifespan (Costa & McCrae, 1992b).
The degree of stability is also related to the initial age of the sample,
as Roberts and DelVecchio (2000) showed. Costa, Parker, and McCrae(2000) reported stability coefficient for 12-year-olds retested at age 16.These ranged from .30 to .63 with a median of 38. R. W . Robins, Fraley ,Roberts, and Trzesniewski (2001) reported on changes over the 4 yearsof college; these somewhat older adolescents were already more stable,showing stability coefficients ranging from .53 to .70 (median = .60).Contrast both of these with the values that Costa, Herbst, et al. (2000)calculated for 40-year-olds retested after 6–9 years, where the medianacross the five personality factors was .83. Adults show much higherstability than early adolescents and substantially higher stability thancollege students.
At what age does personality “stabilize,” that is, reach the maxi-
mum degree of stability for a given retest interval? That is a hotly con-tested question. Based on their meta-analysis, which statistically com-bined every study they could locate in the literature—some 3,000correlations in all—Roberts and DelVecchio estimated that stability co-efficients do not peak until age 50–60 and predicted that retest correla-tions from 40-year-olds should be about .60 over a 7-year interval. Theyargued from this that there is more flexibility in adulthood and morepossibility for growth and change than our earlier writings had sug -
gested.
But there are reasons to be skeptical of these meta-analytic results.
After all, we know from studies of 40-year-olds that the observed stabil -
ity is much higher than .60, at least when the NEO-PI-R is the instru -
ment used (Costa, Herbst, et al., 2000). It turns out that most of the
studies Roberts and DelVecchio had to review were of children and ado -
lescents, which obviously do not bear directly on the issue of stability in
adulthood. And meta-analyses are by design nonevaluative—they com -
bine good and poor studies equally—and by necessity are limited to the
studies that have been published. If there are only a few studies in theliterature and some of them are suboptimal, then no amount of statisti -
cal manipulation can arrive at trustworthy results.
In meta-analyses results are pooled from studies with different114 PERSONALITY IN ADULTHOOD