This is the third and final article in a series ordered for $3.50 USD by 150 IQ Ganzir (the market has since driven the price up to $15). Here, I focus on a 1958 paper on 64 Yeshiva men (age 16 to 31; mean age 21.43). Author Boris M. Levinson states:

Our sample finally consisted of 64 subjects, classified as follows : (a) six senior Yeshiva High School students, (b) 31 Yeshiva College students, (c) 27 graduate students. Among them were four ordained rabbis. Every graduate student was an alumnus of Yeshiva College. The writer believes that the sample secured was fairly representative of the Yeshiva population…

Below are the scores of the sample on the original Wechsler Adult Intelligence Scale (WAIS). The 11 subtest scores are expressed on a scale where the average American scores 10 (SD = 3), and the verbal, performance, and full-scale IQs are expressed on a scale where the average American scores 100 (SD = 15). To convert scaled scores to IQ equivalents, just multiply by 5 and then add 50. Because the study, was submitted for publication in 1957 and the WAIS was standardized in 1953.5, there was a trivial Flynn effect I adjusted for.

After correcting for slightly inflated norms, not a single mean score on the verbal subtests fell below the “Bright Normal range” and not a single performance subtest fell above the Average range. This complete lack of overlap shows the validity of the original verbal vs performance dichotomy that the Wechsler scales have since abandoned but which reflects the likely original reasons human intelligence evolved: To talk (verbal IQ) and to make and use tools (performance IQ).

Even Wechsler himself, who was also a Jewish New Yorker, likely showed this verbal > performance gap, as he became concerned that he could not solve his own Block Design items quickly.

The mean verbal > performance gap in this study is 21 points (22 after I adjust for norm inflation) but Levinson notes that for the graduate student sub-sample (n = 27), the mean gap was about 26 points and for rabbis (n = 4) it was about 34, which he interpreted as evidence that exposure to traditional Jewish culture was causing the gaps.

Levinson writes:

The students stated that the performance items appeared childish and unimportant. While they tried to achieve a good score whenever possible, the verbal items were more of a challenge...They said that an inferior score on a performance test was not as damaging to their self-esteem as a poor mark on the verbal tests.

I had the opposite attitude when I was tested on the Wechsler children’s scale at age 12. I thought the verbal items were mostly measuring what I learned in school and thus not knowing an answer didn’t damage my self-esteem. By contrast I saw the performance items as measuring my real intelligence.

Levinson writes:

In discussing the digit span test, quite a few of them indicated that they had visualized the digits. This is similar to the experience of some of these students who, in studying the Talmud, remember page location of a passage.

On the other hand, practice on one cognitive task seldom transfer to another unless they’re all but identical. In one study people who practiced their memory span for digits managed to increase it from seven to in some case over 100, but when faced with a memory span for letters task. They were right back down to seven. But perhaps that study was too brief to fully capture the effects of practice.

Levinson writes:

The subjects have been subjected, since their early school days, to a curriculum which greatly emphasized verbal knowledge, rote memory, verbal concept formation, abstract ideas, to the general neglect of performance arts. Examinations in the Talmud, for example, are oral and emphasize the detailed memorization and understanding of tracts. A differentiation of intellectual abilities has thus occurred. These cultural forces have also brought about different attitudes and self concepts regarding various intellectual tasks. Failure on a performance item does not carry the same ego deflating connotations as failures on a verbal task. It thus appears that the greater the premium placed on verbal ability in a subculture, the greater will be the disparity between verbal and performance WAIS scores.

There’s no doubt that cultural exposure affects verbal IQ score. Excellent research in the 1920s showed that canal boat children who lived a nomadic existence where they were virtually deprived of schooling, showed massive declines in IQ as they got older. Because IQ tests are normed for age, and because these kids were kept out of school they fell further and further behind their chronological age-mates on the type of knowledge that IQ tests measure. Young canal boat kids would have an IQ around 90, but older canal boat kids would have an IQ of 60. However when their performance IQs were tested, there was no such decline.

Perhaps the opposite is occurring with Yeshiva kids. Instead of their verbal IQs falling further and further behind as the effects of missed schooling accumulate, they grow further and further ahead, as the effects of enhanced schooling multiply.

On the other hand schooling likely has diminishing returns on verbal IQ once we get a basic amount. A study in Japan (where schooling is more intense) found older kids scored only slightly higher on verbal IQ.