range is such that ordinarily
intelligent adults, little educated, test up to what is called the
"average adult" level. Adults whose intelligence is known from other
sources to be superior are found to test well up toward the "superior
adult" level, and this holds whether the subjects in question are well
educated or practically unschooled. The almost entirely unschooled
business men, in fact, tested fully as well as high-school juniors and
seniors.

Figure 1 shows the distribution of mental ages for 62 adults, including
the 30 business men and the 32 high-school pupils who were over 16 years
of age. It will be noted that the middle section of the graph represents
the "mental ages" falling between 15 and 17. This is the range which we
have designated as the "average adult" level. Those above 17 are called
"superior adults," those between 13 and 15, "inferior adults." Subjects
much over 15 years of age who test in the neighborhood of 12 years may
ordinarily be considered border-line cases.

[Illustration: FIG. 1. DISTRIBUTION OF MENTAL AGES OF 62 NORMAL ADULTS]

The following method was employed for determining the validity of a
test. The children of each age level were divided into three groups
according to intelligence quotient, those testing below 90, those
between 90 and 109, and those with an intelligence quotient of 110 or
above. The percentages of passes on each individual test at or near that
age level were then ascertained separately for these three groups. If a
test fails to show a decidedly higher proportion of passes in the
superior I Q group than in the inferior I Q group, it cannot be regarded
as a satisfactory test of intelligence. On the other hand, a test which
satisfies this criterion must be accepted as valid or the entire scale
must be rejected. Henceforth it stands or falls with the scale as a
whole.

When tried out by this method, some of the tests which have been most
criticized showed a high degree of reliability; certain others which
have been considered excellent proved to be so little correlated with
intelligence that they had to be discarded.

After making a few necessary eliminations, 90 tests remained, or 36 more
than the number included in the Binet 1911 scale. There are 6 at each
age level from 3 to 10, 8 at 12, 6 at 14, 6 at "average adult," 6 at
"superior adult," and 16 alternative tests. The alternative tests, which
are distributed among the different groups, are intended to be us