Personality psychologists should also be concerned with the credibility of
the numbers generated by their tests. Personality assessment is a central part
of personality research. If we are going to study achievement motivation,
self-esteem, social anxiety, and so on, we need to measure these concepts as
accurately as possible. Similarly, psychologists working in education, human
resources, and counseling often rely on personality tests to determine whether
a child should be placed in a special class, whether an employee should be
promoted to a new position, or whether a client needs to be admitted to apsychiatric hospital.
In each case, it is the responsibility of the people using the test to see that it
accurately measures the concept they are interested in. Unfortunately, not allpersonality tests are as good as psychologists would prefer, and even the best
tests can be used inappropriately. So how can we tell a good test from a bad
one or determine whether the test measures what we want to measure? Beforeusing any standardized test, we need to examine its reliability andvalidity.
Reliability
Suppose you took a personality test today and it indicated that, compared to
others your age, you scored high on independence . That is, more than most
people, you enjoy being on your own and making your own decisions.
However, suppose next week you take the test again, and this time your score
indicates you are relatively low on independence. Which of these scores re-
flects your true personality? Unfortunately, you have no way to know fromthis test whether you are an independent or a dependent person. The test suf-
fers from poor reliability.
A test has good reliability when it measures consistently. One indication
of a test ’s reliability is how consistently the test measures over time. Many
factors can contribute to poor consistency over time. The test questions or
the scoring procedures might be vague, or perhaps test responses fluctuatewildly depending on the test taker ’s mood. Nonetheless, because we assume
personality is relatively consistent over time, tests designed to measure per-
sonality must provide consistent scores over time.
A common way to determine a test ’s consistency is to calculate a test–
retest reliability coefficient. Researchers first administer the test to a large
number of people. Some time later, usually after a few weeks, the same peo-
ple take the test again. The scores from the first administration are corre-
lated with those from the second. Recall that correlation coefficients can
range from 1.00 to /C01.00. A high positive correl ation coefficient indicates
good consistency over time.
Unfortunately, whether a test is reliable is not a simple yes-or-no ques-
tion. On one hand, a test –retest coefficient of .90 is probably reliable enough
to meet most people ’s needs. On the other hand, a reliability coefficient of .20
is no doubt too low for most purposes. But what about something in be-
tween? Is a test with a reliability coefficient of .50 or .60 acceptable? The an-
swer depends on the researcher ’s needs and the availability of alternative,
more reliable tests. Sometimes the nature of the concept being measuredcontributes to low reliability. For example, tests given to young children,“The man with crea-
tive ideas in philoso-
phy or art can give
wings to them at
once; but in science …
extensive painstaking
experiment has to be
done.”
Raymond Cattell34 CHAPTER 2 Personality Research Methods