The Mismeasure of Man by Stephen Jay Gould

(^248) THE MISMEASURE OF MAN
INFECTED NOT INFECTED
White Alpha
White Beta
Negro Alpha
Negro Beta
94.38
45.38
34.86
22.14
118.5 0
53.26
40.82
26.09
These results might have led to the obvious admission that state of
health, particularly in diseases related to poverty, has some effect
upon the scores. Although Yerkes did not deny this possibility, he
stressed another explanation (p. 811): "Low native ability may
induce such conditions of living as to result in hookworm infec-
tion."
In studying the distribution of scores by occupation, Yerkes
conjectured that since intelligence brings its own reward, test scores
should rise with expertise. He divided each job into apprentices,
journeymen, and experts and searched for increasing scores
between the groups. But he found no pattern. Instead of abandon-
ing his hypothesis, he decided that his procedure for allocating
men to the three categories must have been flawed (pp. 831-832):
It seems reasonable to suppose that a selection process goes on in
industry which results in a selection of the mentally more alert for pro-
motion from the apprentice stage to the journeyman stage and likewise
from the journeyman stage to the expert. Those inferior mentally would
stick at the lower levels of skill or be weeded out of the particular trade.
On this hypothesis one begins to question the accuracy of the personnel
interviewing procedure.
Among major patterns, Yerkes continually found relationships
between intelligence and amount of schooling. He calculated a cor-
relation coefficient of 0.75 between test score and years of educa-
tion. Of 348 men who scored below the mean in Alpha, only 1 had
ever attended college (as a dental student), 4 had graduated from
high school, and only 10 had ever attended high school at all. Yet
Yerkes did not conclude that more schooling leads to increasing
scores per se; instead, he argued that men with more innate intel-
ligence spend more time in school. "The theory that native intelli-
gence is one of the most important conditioning factors in
continuance in school is certainly borne out by this accumulation
of data" (p. 780).