Time 2. It is principally for this reason that we would not want to con -
duct a study in which only Extraversion was measured at two times: If
the heterotypic continuity model is correct, we would miss importantevidence of personality continuity and transformation because wewould not have assessed the trait into which Extraversion metamor -
phosed. By measuring all five personality factors, we are in a position to
give a definitive test of the heterotypic continuity model in adulthood.
The balancing model of personality development is somewhat eas -
ier to evaluate, because we know the direction of the change we are sup -
posed to expect. If we measure traits at the beginning of adulthood and
then again at the end, we would expect a strong correlation betweencorresponding measurements of each trait—but we would hypothesizethat the correlation would be negative . The extreme introvert would
have become the extreme extravert; the feminine person would have be -
come masculine; the open individual would have become closed. The
predictions of this model, however, are somewhat harder to anticipate ifthe time span between measurements is a matter of years instead of de-cades, since individuals may not yet have reached the hypotheticalcrossover point. We would, however, expect great variability among in-dividuals at the beginning and end of adulthood, but similarity amongthe middle aged, all of whom are nearing the central crossover point.
Finally , the predictions of the stability model are straightforward: If
personality traits are relatively unchanging over the years, there shouldbe high positive correlations between corresponding traits over the twotimes; and the correlations of each trait with itself over time should behigher than the correlations across time between different traits. Inother words, the same pattern that we call retest reliability when the testis readministered after a month would be seen as stability of personalityif it were readministered after a decade.
Longitudinal Evidence
Many of the studies we described in Chapter 4 as sources of longitudi -
nal evidence about changes in the average levels of traits have also pro -
vided evidence about the course of traits in individuals. Let us begin
with an examination of data from the BLSA for the 114 men who tookthe GZTS on three occasions about 6 years apart (Costa, McCrae, &Arenberg, 1980). Table 11 gives the observed intercorrelations amongthe 10 traits across 12 years from the first to the third administration.108 PERSONALITY IN ADULTHOOD