THE HEREDITARIAN THEORY OF IQ 247vidual who fails to earn a positive score and is marked zero is actually
thereby given a bonus varying in value directly with his stupidity (p. 622).
Boring therefore "corrected" each zero score by calibrating it
against other tests in the series on which the same man had scored
some points. If he had scored well on other tests, he was not doubly
penalized for his zeros; if he had done poorly, then his zeros were
converted to negative scores.
By this method, a debilitating flaw in Yerkes's basic procedure
was accentuated by tacking an additional bias onto it. The zeros
only indicated that, for a suite of reasons unrelated to intelligence,
vast numbers of men did not understand what they were supposed
to do. And Yerkes should have recognized this, for his own reports
proved that, with reduced confusion and harassment, men who
had scored zero on the group tests almost all managed to make
points on the same or similar tests given in an individual examin-
ation. He writes (p. 406): "At Greenleaf it was found that the pro-
portion of zero scores in the maze test was reduced from 28
percent in Beta to 2 percent in the performance scale, and that
similarly zero scores in the digit-symbol test were reduced from 49
to 6 percent."
Yet, when given an opportunity to correct this bias by ignoring
or properly redistributing the zero scores, Yerkes's statisticians did
just the opposite. They exacted a double penalty by demoting most
zero scores to a negative range.
FINAGLING THE SUMMARY STATISTICS:
GETTING AROUND OBVIOUS CORRELATIONS WITH ENVIRONMENT
Yerkes's monograph is a treasure-trove of information for any-
one seeking environmental correlates of performance on "tests of
intelligence." Since Yerkes explicitly denied any substantial causal
role to environment, and continued to insist that the tests mea-
sured innate intelligence, this claim may seem paradoxical. One
might suspect that Yerkes, in his blindness, didn't read his own
information. The situation, in fact, is even more curious. Yerkes
read very carefully; he puzzled over every one of his environmen-
tal correlations, and managed to explain each of them away with
arguments that sometimes border on the ridiculous.
Minor items are reported and dispersed in a page or two.
Yerkes found strong correlations between average score and infes-
tation with hookworm in all 4 categories: