It is only the ratio of retardation or acceleration
to chronological age (that is, the I Q) which has significance.

It follows also that if the I Q is a valid expression of intelligence,
as it seems to be, then the Binet-Simon "age-grade method" becomes
transformed automatically into a "point-scale method," if one wants to
use it that way. As such it is superior to any other point scale that
has been proposed, because it includes a larger number of tests and its
points have definite meaning.[22]

[22] For discussion of the supposed advantages of the "point-scale
method," see Yerkes and Bridges: _A New Point Scale for Measuring Mental
Ability_. (Warwick and York, 1915.)

SEX DIFFERENCES. The question as to the relative intelligence of the
sexes is one of perennial interest and great social importance. The
ancient hypothesis, the one which dates from the time when only men
concerned themselves with scientific hypotheses, took for granted the
superiority of the male. With the development of individual psychology,
however, it was soon found that as far as the evidence of mental tests
can be trusted the _average_ intelligence of women and girls is as high
as that of men and boys.

If we accept this result we are then confronted with the difficult
problem of finding an explanation for the fact that so few of those who
have acquired eminence in the various intellectual fields have been
women. Two explanations have been proposed: (1) That women become
eminent less often than men simply for lack of opportunity and stimulus;
and (2) that while the average intelligence of the sexes is the same,
extreme variations may be more common in males. It is pointed out that
not only are there more eminent men than eminent women, but that
statistics also show a preponderance of males in institutions for the
mentally defective. Accordingly it is often said that women are grouped
closely about the average, while men show a wider range of distribution.

[Illustration: FIG. 3. MEDIAN I Q OF 457 BOYS (UNBROKEN LINE) AND
448 GIRLS (DOTTED LINE) FOR THE AGES 5-14 YEARS]

Many hundreds of articles and books of popular or quasi-scientific
nature have been written on one aspect or another of this question of
sex difference in intelligence; but all such theoretical discussions
taken together are worth less than the results of one good experiment.
Let us see what our 1000 I Q's have to offer toward a solution of the
problem.

1. When the I Q's