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The Role of Intelligence in Modern Society

Are social changes dividing us into intellectual haves and have-nots? The question pushed aside in the 1970s is back, and the issues are far from simple

Earl Hunt

How Important Is Intelligence?

No one would worry about who has intelligence, or why, if it did not matter. Indeed, one of the claims made by the opponents of testing in the 1960s and 1970s was that intelligence tests just measured academic performance, and that even there they did not do a good job. One of Herrnstein and Murray's major contributions has been to expose this bit of Mokita. Intelligence, as measured by the tests, really does matter in both school and workplace, although it may matter in somewhat different ways than The Bell Curve suggests.

To argue that IQ is a determinant of economic outcomes, Herrnstein and Murray relied on two sources of evidence. One was the recent literature, and especially John Hunter's (1986) summary of the relation between IQ scores and workplace performance. The other was their own analysis of data from the National Longitudinal Survey of the Labor Market Experience of Youth (NLSY). The NLSY is a Department of Labor survey that has followed over 12,000 participants since 1979. The respondents are now in their late 20s and early 30s. Early in the survey many participants took the Department of Defense's ASVAB test. Herrnstein and Murray used the AFQT score, which is derived from the ASVAB subtest scores, as a measure of IQ. They then related IQ to subsequent life events, such as being employed or being below the official poverty line.

Hunter reviewed studies of the relationship between job performance and scores on the General Aptitude Test Battery (GATB), a Department of Labor test which was widely used until the late 1980s, when the testing program became embroiled in a controversy over its fairness to minorities. The GATB was withdrawn as a political rather than a scientific decision. After a detailed statistical analysis, Hunter concluded that the "true" relation between intelligence and job performance in the population is about 0.5. This conclusion depended heavily upon extrapolating relationships beyond the data, which assumes linearity. A National Science Committee reviewing the GATB argued that Hunter should have used the observed correlations, which were almost all in the 0.2 to 0.3 range. The truth probably lies between these estimates, providing that the extrapolation is to comparable jobs (Hunt 1995). And that is an important qualification.

The GATB was designed to screen applicants for entry-level jobs in blue-collar and lower-level white-collar occupations. In terms of averages (something that is well established), we are talking about occupations where the mean IQ is in the 90-110 range, which covers about half of the population. But recall that as intelligence goes up cognitive abilities become more differentiated. Also, as experience goes up the IQ-performance connection gets weaker. These factors would lead to a reduction in IQ-performance relations within higher-level job classifications, and when dealing with experienced and older individuals. (In fact, the GATB is known to be less accurate in predicting the performance of older workers.)

The qualification within a job class is also important. There are quite high correlations between the socioeconomic status of a job and the mean IQ of the jobholders. Truck drivers average slightly under 100, while high-paid professionals, such as doctors and lawyers, have averages of 125 or above. It is sometimes asserted that this is because general intelligence is needed to obtain the educational certification required to qualify for a job, but is less important to on-the-job performance. There is evidence for this. Military and civilian studies have found that IQ tests are better predictors of performance when people are in training programs than when they are on the job itself. After people are on the job, correlations are higher between IQ and tests of job knowledge than between IQ and on-the-job observations of performance. However, none of the correlations vanish.

IQ does not predict all aspects of job performance. In an extensive study of enlisted personnel (Campbell, McHenry and Wise 1990), the Army found that it was useful to distinguish between what might be called ability aspects of performance, which includes such things as knowledge of one's job requirements and the ability to operate machinery required in the job, and motivational aspects, which include cooperating with colleagues, showing initiative and leadership. The ASVAB did a good job of predicting the ability aspects but had almost no relation to the motivational aspects. This is not surprising, but it does make any focus on a unitary index of job competence seem simplistic.

In summary, it appears that IQ is an important factor in getting into a job or profession, but is less important (although not negligible) once you have learned to do the job. Further improvement is then achieved by acquiring experience, rather than improving upon an abstract knowledge of what the job requires.

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