Bell Curve

74 The Emergence ofa Cognitive Elite The Economic Pressure to Partition 75The Validity of the AFQT for Military TrainingMean Validity ofAFQT Score andMilitary Job FamilyTraining SuccessMechanical .62Clerical .58Electronic +67General technical -62Source: Hunter 1985, Table 3.jor job families are shown in the table above. These results are basedon results from 828 military schools and 472,539 military personnel,The average validity was .62. They hold true for individual schools aswell. Even the lowest-validity school, combat, in which training suc.cess is heavily dependent on physical skills, the validity was still a substantial.45.[*01The lowest modern estimate of validity for cognitive ability is theone contained in the report by a panel convened by the National Academyof Sciences, Fairness in Employment ~estin~." That report concludedthat the mean validity is only about .25 for the GATB, in contrast tothe Hunter estimate of .45 (which we cited earlier), Part of the reasonwas that the Hartigan committee (we name it for its chairman, Yale statisticianJohn Hartigan), analyzing 264 studies after 1972, concludedthat validities had generally dropped in the more recent studies. But themain source of the difference in validities is that the committee declinedto make any correction whatsoever for restriction of range (see aboveand note 6). It was, in effect, looking at just the tackles already in theNFL; Hunter was considering the population at large. The Hartigancommittee's overriding concern, as the title of their report (Fairness inEmployment Testing) indicates, was that tests not be used to exclude people,especially blacks, who might turn out to be satisfactory workers.Given that priority, the committee's decision not to correct for restrictionof range makes sense. But failing to correct for restriction of rangeproduces a misleadingly low estimate of the overall relationship of IQto job performance and its economic consequences.[221 Had the Hartigancommittee corrected for restriction of range, the estimates of therelationship would have been .35 to .40, not much less than Hunter's.THE REASONS FOR THE LINK BETWEEN COGNITIVE ABILITYAND JOB PERFORMANCEWhy are job performance and cognitive ability correlated? Surgeons, forexample, will be drawn from the upper regions of the IQ distribution.But isn't it possible that all one needs is "enough" intelligence to be asurgeon, after which "more" intelligence doesn't make much difference?Maybe small motor skills are more important. And yet "more" intelligencealways seems to be "better," for large groups of surgeons and everyother profession. What is going on that produces such a result?Specific Skills or g?As we begin to explore this issue, the story departs more drastically fromthe received wisdom. One obvious, commonsense explanation is thatan IQ test indirectly measures how much somebody knows about thespecifics of a job and that that specific knowledge is the relevant thingto measure. According to this logic, more general intellectual capacitiesare beside the point. But the logic, however commonsensical, iswrong. Surprising as it may seem, the predictive power of tests for jobperformance lies almost completely in their ability to measure the mostgeneral form of cognitive ability, g, and has little to do with their abilityto measure aptitude or knowledge for a particular job.SPECIFIC SKILLS VERSUS G IN THE MILITARY. The most complete data onthis issue come from the armed services, with their unique advantagesas an employer that trains hundreds of thousands of people for hundredsof job specialties. We begin with them and then turn to the correspondingdata from the civilian sector.In assigning recruits to training schools, the services use particularcombinations of subtests from a test battery that all recruits take, theArmed Services Vocational Aptitude Battery (ASVAB).'~] The Pentagon$psychometricians have tried to determine whether there is anypractical benefit of using different weightings of the subtests for different jobs rather than, say, just using the overall score for all jobs Theoverall score is itself tantamount to an intelligence test. One of the mostcomprehensive studies of the predictive power of intelligence tests wasby Malcolm Ree and James Earles, who had both the intelligence testscores and the final grades from military school for over 78,000 air force