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

afternoon, defining in terms of use, drawing designs from memory, 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