material might miss one particular item for any number of reasons. But over
the course of, say, 50 items, the student who knows the material is likely toget a higher score than the student who does not. In psychometric terms, the
50-item test has a greater internal consistency (Chapter 2) and is thus a better
indicator of the student ’s knowledge. Unfortunately, at the time Mischel
launched his attack, many trait studies measured behavior with what were es-
sentially one-item tests. A personality trait may be a good predictor of behav-
ior, but psychologists will never know if they don ’t measure behavior reliably.
As an alternative to one-item measurement, researchers can aggregate
data. For example, if you want to measure how much time students spendstudying, you’ ll obtain a much better score by observing their behavior each
night over the course of a few weeks than by observing just one night.
Consider a study in which scores on an extraversion scale were used to pre-
dict social behavior (Epstein, 1979). Undergraduates in this study recordedthe number of social contacts they initiated each day. Although we would ex-
pect extraverts to initiate more social contacts than introverts, the researchers
found an insignificant correlation between any one day ’s total of social con-
tacts and extraversion scores. However, when the researchers looked at the
relation between the scale score and the student ’s 2-week total of initiated so-
cial contacts, they found an impressive correlation of .52. Another investiga-
tion looked at trait measures of aggression and the number of aggressive acts
students performed (e.g., getting into an argument, yelling at someone) over
the course of 2 weeks (Wu & Clark, 2003). The researchers found a correla-
tion of .51 between the aggregated aggression measure and the trait score.
Identifying Relevant Traits
Another reason personality trait measures usually fail to break the .30 to .40
barrier is that researchers may be looking at the wrong traits. Recall Allport ’s
distinction between central and secondary traits. A trait is more likely to pre-
dict a person ’s behavior if that trait is important, or central, for the person.
Suppose you were interested in the trait independence . You might give an in-
dependence scale to a large number of people, and then correlate the scores
with how independently people acted in some subsequent situation. But in
doing this, you probably would group together those people for whom inde-pendence is an important (central) trait and those for whom it is a relatively
unimportant (secondary) trait. You undoubtedly would do better predicting
independent behavior by limiting your sample to people who consider inde-pendence an important personality dimension. By including people for whom
the trait is only secondary, you dilute the correlation between the trait score
and the behavior (Britt & Shepperd, 1999).
To illustrate this problem, one team of researchers identified people who
were either fairly consistent or relatively inconsistent in two kinds of behav-
ior, friendliness and conscientiousness (Bem & Allen, 1974). Some personalityresearchers refer to these two groups as traited anduntraited people because
the personality trait is either an important one for them or insignificant. The
goal of this study was to predict six measures of friendly behavior (for exam-
ple, how friendly the participant was while waiting for the experiment to168 CHAPTER 7 The Trait Approach