who often fluctuate in mood and attention, frequently have lower than desir-
able levels of reliability.
Another aspect of reliability is internal consistency . A test is internally con-
sistent when all the items on the test measure the same thing. Let ’s say 10 items
on a 20-item test of extraversion accurately measure the extent to which a testtaker is an extraverted person. Because half the items measure extraversion, the
overall score probably is somewhat indicative of the person ’s true level on this
trait. But because half the items measure something besides extraversion, the use-
fulness of the score is limited. This test suffers from poor internal consistency.
Once again, statistical tests are available to help us determine how well
responses on one test item correlate with responses on the other items. A sta-tistic called an internal consistency coefficient can be calculated. A high coef-
ficient indicates that most of the items are measuring the same concept; a lowcoefficient suggests items are measuring more than one concept. A careful testmaker includes in the final version of a test only those items that “hang to-
gether ”to measure the same concept.
Validity
Reliability data tell us whether a test is measuring something consistently. Butthey tell us nothing about what the test is measuring. That is why psychologists
also examine data concerning the test ’s validity. Validity refers to the extent to
which a test measures what it is designed to measure. As with reliability, the
question is not whether a test does or does not have validity. Rather, the ques-
tion is how well the validity of the test has been demonstrated.
Validity is relatively easy to determine for some kinds of tests. For exam-
ple, if the purpose of a test is to predict how well students will do on an up-coming task, researchers can simply compare the test scores with the task
scores to determine the predictive validity of the test. Unfortunately, demon-
strating validity for most personality tests is not so easy. Personality psycholo-
gists often are interested in measuring hypothetical constructs, such as
intelligence, masculinity, or social anxiety. Hypothetical constructs are useful
inventions researchers employ to describe concepts that have no physical real-
ity. That is, no one can be shown an intelligence. We can see behavior that sug-
gests high intellectual functioning, but intelligence remains a theoretical entity.
The problem for personality researchers, then, is how to demonstrate that
a test measures something that, in reality, is but a useful abstract invention.
How do we know if a test measures self-esteem? Test takers who agree with
the item, “I am not as competent in sports as most people, ”might have low
self-esteem. Then again, they might just have poor athletic ability, or they
might be depressed. Fortunately, there is much personality researchers can do
to demonstrate the construct validity of a test. Researchers can look at a
test’s face validity, congruent validity, discriminant validity, and behavioral
validation.
Face Validity
Perhaps the most obvious way to decide if a test measures what it says it
measures is to look at the test items. Most of us would accept that a testPersonality Assessment 35