226 THE MISMEASURE OF MANogist himself but then Yerkes's lieutenant (and the army's captain),
selected one hundred sixty thousand cases from the files and pro-
duced data that reverberated through the 1920s with a hard here-
ditarian ring. The task was a formidable one. The sample, which
Boring culled himself with the aid of only one assistant, was very
large; moreover, the scales of three different tests (Alpha, Beta,
and individual) had to be converted to a common standard so that
racial and national averages could be constructed from samples of
men who had taken the tests in different proportions (few blacks
took Alpha, for example).
From Boring's ocean of numbers, three "facts" rose to the top
and continued to influence social policy in America long after their
source in the tests had been forgotten.
- The average mental age of white American adults stood just
above the edge of moronity at a shocking and meager thirteen.
Terman had previously set the standard at sixteen. The new figure
became a rallying point for eugenicists who predicted doom and
lamented our declining intelligence, caused by the unconstrained
breeding of the poor and feeble-minded, the spread of Negro
blood through miscegenation, and the swamping of an intelligent
native stock by the immigrating dregs of southern and eastern
Europe. Yerkes* wrote:
It is customary to say that the mental age of the average adult is about
16 years. This figure is based, however, upon examinations of only 62
persons; 32 of them high-school pupils from 16-20 years of age, and 30
of them "business men of moderate success and of very limited educational
advantages." The group is too small to give very reliable results and is
furthermore probably not typical. ... It appears that the intelligence of
the principal sample of the white draft, when transmuted from Alpha and
Beta exams into terms of mental age, is about 13 years (13.08) (1921, p.
785)-
Yet, even as he wrote, Yerkes began to sense the logical absurdity
of such a statement. An average is what it is; it cannot lie three
years below what it should be. So Yerkes thought again and added:
We can hardly say, however, with assurance that these recruits are
three years mental age below the average. Indeed, it might be argued on
*I doubt that Yerkes wrote all parts of the massive 1921 monograph himself. But
he is listed as the only author of this official report, and I shall continue to attribute
its statements to him, both as shorthand and for want of other information.