Intelligence: In Pursuit of Rational Thought and Effective Action 147
paring paired scores for each child in the group, a high score on Form A should
predict a high score on Form B. And a low score on Form A should predict a
low score on Form B. If these predictions aren’t obtained, then the test is not
reliable.
A test is one that gives stable, repeatable results.
Answer: reliable.
The two related factors of validity and reliability generate four possibilities
for any kind of measuring instrument. The instrument may be (1) neither valid
nor reliable, (2) valid, but not reliable, (3) reliable, but not valid, (4) both valid
and reliable. This fourth happy circumstance is the one we usually associate
with rulers, clocks, and thermometers. These are the primary measuring instru-
ments of physics. They are some of the reasons why it has such a high status as
a science.
In psychology, both personality tests and intelligence tests are forced to deal
with the mutual problems of validity and reliability. Fortunately, with the use of
the correlation coefficient applied to large sets of scores, a reasonable level of
validity and reliability can be obtained. The Stanford-Binet Intelligence Scale and
the Wechsler Scales have been subjected to a substantial amount of scrutiny and
evaluation. On the whole, they are considered to be both valid and reliable meas-
uring instruments.
The two related factors of validity and reliability generated how many possibilities for any
kind of measuring instrument?
Answer: Four.
The Interaction of Heredity and Environment: How They
Exert Joint Effects
What is the primary determinant of intelligence? Is it heredity? Is it environment?
Or, is it possible that the best answer can’t be given in either-or terms?
The topic under discussion in this section is sometimes called the nature-
nurture controversy,and it has a long history in philosophy, biology, and psy-
chology. Nature refers to heredity; the primary characteristic of nature, or
heredity, is the potentialto reach a given level of intelligence. Nurture,on the
other hand, refers to environment; the primary characteristic of nurture, or envi-
ronment, is its capacity to bring forth, in the case of intelligence, the maximum
cognitive potential that an individual has. Or, conversely, environment has the
capacity to inhibit and restrict that potential.
