association, the size of correlations typically found in that field of re -
search, and the reliability of the measuring instruments.
In a few cases standards have become generally accepted. Reliabil -
ity coefficients for personality tests, for example, are supposed to be in
the vicinity of .70 to .90; most researchers would look askance at a testwhose internal consistency was .40. In the prediction of behavior from apersonality test, on the other hand, .40 would be quite respectable. Onestatistician, Jacob Cohen (1969), offered his expectations for psycho -
logical research in a set of rules of thumb: .10 is small; .30 is moderate;
.50 or better is a large correlation. It may be useful to the reader to con -
sider a few familiar examples. The correlation of aptitude tests with col -
lege grades is about .40–.60 (Edwards, 1954); height and weight show a
correlation of roughly .70 (Peatman, 1947); and self-reports of anxietyand depression correlate about .60 in the Baltimore Longitudinal Studyof Aging (BLSA).
If we obtain a set of measurements of personality traits and several
years later measure the same set of people once more on the same set oftraits, we would have the minimum information necessary to begin toevaluate the alternative theoretical positions we have described above.From the correlation of each trait at the first time with each trait at thesecond, we could test quite specific hypotheses about personality devel-opment.
If the environmentalist position is correct in positing that personal-
ity is freely reshaped by changing circumstances, there should be littleor no correlation between any of the traits at the first time and any ofthe traits at the second. If sufficient time has elapsed to allow many in -
dividuals in the sample to move, change jobs, marry , or have children,
we should expect substantial change in personality for many people inunpredictable directions. Thus, personality at Time 2 should be unre -
lated to personality at Time 1. We might expect modest correlations
(say , .30) between corresponding traits at the two times because someindividuals would have remained in the same environments, whichmight have sustained the traits.
The heterotypic continuity model would predict high correlations
somewhere, but it might not be possible to predict just where theywould occur. Extraversion at Time 1 might be strongly correlated atTime 2 with Openness or with Agreeableness or with Conscientious -
ness. The distinctive feature of this model is that we would notexpect
Extraversion at Time 1 to be correlated chiefly with Extraversion atThe Course of Personality Development 107