Ch. 6: A Question of Intelligence

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In 1912 the German psychologist Wilhelm Stern proposed dividing the mental age of a child by his chronological age to establish an overall indicator of intelligence. In 1916 American psychologist Lewis Terman introduced the IQ as the scale of scoring for his hugely successful Stanford Revision of the Binet Scales, the famous "Stanford Binet." David Wechsler later developed the IQ tests most widely used today. He dropped the "mental age" concept and used instead the relation of an individual's IQ score to the average IQ score for his age -- calling it "deviation IQ."

The critics of IQ testing were quick to point out that IQ is an abstract concept that may have no bearing on the real world. They quoted Dr. Edward Boring of Harvard, who wrote in 1923, "Intelligence as a measurable capacity must at the start be defined as the capacity to do well in an intelligence test. Intelligence is what the tests test."

The statement is fundamentally true, but the same could be said of all tests. After all, a driver's license test determines only how well an individual does on the test, not necessarily how well he drives. However, no one would seriously argue that people who fail the driving test, on average, drive as well as those who have perfect scores.

Arthur R. Jensen, professor of Educational Psychology at the University of California at Berkeley, in expanding the work of pioneering English psychologist Charles Edward Spearman, substantiated the fact that all tests of mental ability have positive correlation with each other.22 If a person scores below average in one type of mental-abilities test, he is likely to score below average in another type. Conversely, if he is above average in one, he is likely to score similarly high in another. Those who do well in reading, for instance, usually do well in math. The concept of the importance of general intelligence, or "g" intelligence as it is known academically, is accepted by a large majority of scholars and authorities in psychology.

The best way to determine whether IQ testing measures an important factor in relation to achievement is to compare large numbers of individuals' test scores with their later achievements in school and career, comparing how they match up.

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The Bell Curve also shows that IQ has a strong correlation with a number of educational and societal factors, including grades in school, educational level attained, income, business success, and even social factors such as tendencies toward criminality, illegitimacy, and welfare dependence.

Another famous study examined the careers of similarly educated brothers who grew up together in Kalamazoo, Michigan Kalamazoo has been testing all of its public school students since 1924 and offers a wealth of information The studies showed that for brothers who had the same education and same family life, the young brothers, with an IQ difference of 15 points between them, averaged a 14 percent difference in income at middle age, with the high-IQ brother having the higher income.

Job performance and productivity correlate with IQ the same way that personal success and income do. In the December 1986 Journal of Vocational Behavior, John E. Hunter, an industrial psychologist at Michigan State University, disclosed that high-complexity job performance correlated .58 with IQ scores. Even in low-skill jobs, intelligence correlated to overall job performance by .23. [Correlation measures how closely two properties are connected. A correlation of +1 means perfect association and 0 means they are completely independent. When the correlation is -1 that means that when one increases, the other always falls.]

Hunter argues that in all jobs intelligence predicts performance, but the factor is even more important in high-complexity occupations. From the classic studies mentioned above, to the latest research of the '90s, the results are overwhelmingly consistent, intelligence does matter.

For all the high-minded language used by the egalitarian politicians and the U.S. Government, the commanders of the United States military readily accept the link between intelligence and later performance. Military authorities give every recruit what it calls an Armed Forces Qualification Test (AFQT). They don't call it an IQ test, but it does measure mental ability and is, in essence, an IQ test. Linda Gottfredson has pointed out that the military is prohibited by law (except under a declaration of war) from enlisting recruits below the 10th percentile level.

That law was enacted because of the extraordinary high training costs and high rates of failure among such men during the mobilization of forces in World War II. A U.S. Department of Defense report states, "People with high AFQT scores are likely to achieve skill proficiency earlier in their first enlistment than those with low scores."

An example of how powerfully IQ affects different areas of society can be seen in automobile accident rates. Australian psychologist Brian O'Toole showed a powerful inverse correlation between IQs and accident mortality rates. In a study of 46,166 men who previously served in the Australian armed forces, he found that those who had scores in the Army General Classification Test correlated to IQs of between 80-85, had almost three times the death rate due to motor vehicle accidents than those who scored in the 100-115 range. The mortality figures may be even more extreme for even lower IQ levels, but those who scored lower than an equivalent IQ of 80 were rejected from service, so there were no records for them. O'Toole wrote: "[P]eople with lower intelligence may have a poorer ability to assess risks and, consequently, may take more poor risks in their driving than do more intelligent people."

As I delved deeper into the IQ issue in the mid-'60s, I was amazed at the difference between the media discussion of the IQ controversy and the scientific literature on the subject. I began reading the papers of a number of psychologists who argued quite persuasively for the importance of IQ, but it seemed that these scientists and their studies received very little coverage in the popular media. Instead the media repeatedly suggested that IQ really did not mean anything. The popular media also suggested that only "racists" believe in a strong link between intelligence and heredity. There is a wealth of information on the important role of genetics in intelligence, but the media for the most part still ignores it, and repeatedly parrots the line that "there is no scientific evidence showing that intelligence is inherited." A more untrue statement has never been spoken.