In my last post I cited excellent data showing Jewish Americans have a math IQ of 113, a verbal IQ of 109, a processing speed IQ of 100, a grammar IQ of 100, a memory IQ of 96, and a spatial IQ of 93.  I crudely estimated that a composite score of all of these abilities would yield an IQ of 102.

However I was criticised for giving all of these abilities equal weight, when some are better measures of intelligence than others.  The problem, is deciding how much weight to give each subtest depends on your definition of intelligence.  I define intelligence as the mental ability to adapt, so I tend to give all mental abilities equal weight, because when the environment changes, you never know what mental abilities you’re going to need.  Right now, math IQ, verbal IQ, and social IQ are the most adaptive, but if civilization were to crumble and it were every man for himself, spatial IQ would be key.

Of course some mental abilities are always going to be more important than others.  If you can reason abstractly, you can find general solutions that solve many different specific problems.

As my nineth grade math teacher would say in his Quebec accent “if you are good at math, then that means you are good at logic.”  And if you’re good at logic, you’re good at almost everything because the universe is inherently logical.  Perhaps I should have given math more weight than grammar and processing speed when calculating Jewish IQ.

Psychometrics largely defines intelligence as g, general mental ability.  But as scholar Arthur Jensen noted, there’s a difference between general mental ability and mental ability in general.

You can be high on the mental ability that all mental abilities have in common (g), but what good is it, if you’re still low on most mental abilities, because you lack all the non-g mental variance.  People with fetal alcohol syndrome for example, have normal g, but are so lacking in non-g brain power that they are typically too mentally retarded to adapt and require lifelong assistance.

So while g might be an excellent predictor of adaptive behavior for most people, it fails for sub-groups that have a very different cognitive profile.  So how do we scientifically measure the cognitive ability to adapt?  Ideally, we would need to take a random sample of every problem, every lifeform in the history of our universe has faced, and see if your mental abilities can solve them.  Only then would we know if one has a truly adaptive combination of mental aptitudes.

The great David Wechsler probably understood that intelligence was about adaptability, because he defined it, in part, as the ability to “deal effectively with your environment”.  He selected 11 subtests that he felt collectively measured this construct, and he divided them into a verbal scale and a performance scale.

In his book, The Global Bell Curve (page 117), scholar Richard Lynn cites a study of Canadian Jews tested on the Wechsler.  After adjusting for old norms, they had a verbal IQ of 111, a Performance IQ of 103, and full-scale IQ of 107 (white norms).  Based on the fact that the verbal IQ of 111 was almost identical to the verbal IQ of 109 I cited above, from a large representative sample of U.S. Jews, I believe this Canadian study is also representative of North American Jews.

But why then did the Canadian Jews have a Performance IQ of 103, when the U.S. Jews have a spatial IQ of 93 as mentioned at the start of this article.  I think it’s because pure spatial ability is only one part of Wechsler’s original Performance IQ, which also includes reasoning, common sense, visual alertness, lateral thinking, and social smarts.

A full-scale IQ of 107 is 7 points above the white means and is probably a good estimate for Jewish IQ.  High enough to partly explain their wealth, influence and scholarship, but low enough to explain their somewhat smaller brains and dark Caucasoid ancestry.