The Validity Of The Individual Tests
The validity of each test was checked up by measuring it against the scale as
a whole in the manner described on p. 55. For example, if 10-year-old children having
11-year intelligence succeed with a given test decidedly better than 10-year-old
children who have 9-year intelligence, then either this test must be
accepted as valid or the scale as a whole must be rejected. Since we
know, however, that the scale as a whole has at le
st a reasonably high
degree of reliability, this method becomes a sure and ready means of
judging the worth of a test.
When the tests were tried out in this way it was found that some of
those which have been most criticized have in reality a high correlation
with intelligence. Among these are naming the days of the week, giving
the value of stamps, counting thirteen pennies, giving differences
between president and king, finding rhymes, giving age, distinguishing
right and left, and interpretation of pictures. Others having a high
reliability are the vocabulary tests, arithmetical reasoning, giving
differences, copying a diamond, giving date, repeating digits in reverse
order, interpretation of fables, the dissected sentence test, naming
sixty words, finding omissions in pictures, and recognizing absurdities.
Among the somewhat less satisfactory tests are the following: repeating
digits (direct order), naming coins, distinguishing forenoon and
aesthetic comparison. Binet's "line suggestion" test correlated so little
with intelligence that it had to be thrown out. The same was also true
of two of the new tests which we had added to the series for try-out.
Tests showing a medium correlation with the scale as a whole include
arranging weights, executing three commissions, naming colors, giving
number of fingers, describing pictures, naming the months, making
change, giving superior definitions, finding similarities, reading for
memories, reversing hands of clock, defining abstract words, problems of
fact, bow-knot, induction test, and comprehension questions.
A test which makes a good showing on this criterion of agreement with
the scale as a whole becomes immune to theoretical criticisms. Whatever
it appears to be from mere inspection, it is a real measure of
intelligence. Henceforth it stands or falls with the scale as a whole.
The reader will understand, of course, that no single test used alone
will determine accurately the general level of intelligence. A great
many tests are required; and for two reasons: (1) because intelligence
has many aspects; and (2) in order to overcome the accidental influences
of training or environment. If many tests are used no one of them need
show more than a moderately high correlation with the scale as a whole.
As stated by Binet, "Let the tests be rough, if there are only enough of