border-line intelligence)
to test at 90, or only slightly below normal.

Three serious consequences came from the too great ease of the original
Binet scale at the lower end, and its too great difficulty at the upper
end:--

1. In young subjects the higher grades of mental deficiency were
overlooked, because the scale caused such subjects to test only a little
below normal.

2. The proportion of feeble-mindedness among adult subjects was greatly
overestimated, because subjects who were really of the 12- or 13-year
mental level could only earn a mental age of about 11 years.

3. Confusion resulted in efforts to trace the mental growth of either
feeble-minded or normal children. For example, by other versions of the
Binet scale an average 5-year-old will show an intelligence quotient
probably not far from 110 or 115; at 9, an intelligence quotient of
about 100; and at 14, an intelligence quotient of about 85 or 90.

By such a scale the true border-line case would test approximately as
follows:--

At age 5, 90 I Q (apparently not far below normal).
At age 9, 75 I Q (border-line).
At age 14, 65 I Q (moron deficiency).

On the other hand, re-tests of children by the Stanford revision have
been found to yield intelligence quotients almost identical with those
secured from two to four years earlier by the same tests. Those who
graded feeble-minded in the first test graded feeble-minded in the
second test: the dull remained dull, the average remained average, the
superior remained superior, and always in approximately the same
degree.[18]

[18] See "Some Problems relating to the Detection of Border-line Cases
of Mental Deficiency," by Lewis M. Terman and H. E. Knollin, in _Journal
of Psycho-Asthemes_, June, 1916.

It is unnecessary to emphasize further the importance of having an
intelligence scale which is equally accurate at all points. Absolute
perfection in this respect is not claimed for the Stanford revision, but
it is believed to be at least free from the more serious errors of other
Binet arrangements.

CHAPTER V

ANALYSIS OF 1000 INTELLIGENCE QUOTIENTS

An extended account of the 1000 tests on which the Stanford revision is
chiefly based has been presented in a separate monograph. This chapter
will include only the briefest summary of some of those results of the
investigation which contribute to the intelligent use of the revision.

THE DISTRIBUTION OF INTELLIGENCE. The question