“One notable finding is that the correlation between IQ and job status is just about as high if the IQ test is given in childhood, decades before people enter the job market, as it is among young adults who are taking an intelligence test after years of education.
The IQ scores they got when they were 7 or 8 years old were about as correlated with the status level of their adult jobs as their adult IQs would have been.
Mostly, relatives occupy neighboring, if not the same, rungs on the job status ladder, and the closer the relationship is, the nearer they are. Such commonplace findings have many possible explanations, but an obvious one that is not mentioned or tested often by social scientists is that since intelligence runs in families and intelligence predicts status, status must run in families. In fact, this explanation somehow manages to be both obvious and controversial.
The biologically related siblings resembled each other in job status, even though they grew up in different homes. And among them, the full siblings had more similar job status than the half siblings. Meanwhile, adoptive siblings were not significantly correlated with each other in job status.
We have been discussing the top decile: everyone with an IQ of 120 or higher. What about people in the even more rarefied cognitive elite, the top fraction of a centile who are so concentrated in a handful of universities during their college years? We have little to tell us exactly what is happening now, but we know what the situation was fifty years ago, through Lewis Terman’s famous study of 1,500 highly gifted children who were born in the early 1900s and followed throughout their lives. Their average IQs were over three standard deviations above the mean, meaning that the Terman sample represented about l/300th of the population. As of 1940, the members of the Terman sample who had finished their schooling were engaged in high-IQ professions at three times the rate of people in the top 10 percent—24 percent for the Terman sample against 8 percent for the top decile in 1940, as the preceding figure shows.
But the relationship of cognitive ability to job performance goes beyond that. A smarter employee is, on the average, a more proficient employee. This holds true within professions: Lawyers with higher IQs are, on the average, more productive than lawyers with lower IQs. It holds true for skilled blue-collar jobs: Carpenters with high IQs are also (on average) more productive than carpenters with lower IQs. The relationship holds, although weakly, even among people in unskilled manual jobs. The magnitude of the relationship between cognitive ability and job performance is greater than once thought.
The smarter employee tends to remain more productive than the less smart employee even after years on the job. An IQ score is a better predictor of job productivity than a job interview, reference checks, or college transcript. Most sweepingly important, an employer that is free to pick among applicants can realize large economic gains from hiring those with the highest IQs. An economy that lets employers pick applicants with the highest IQs is a significantly more efficient economy.
Cognitive ability itself—sheer intellectual horsepower, independent of education—has market value. Seen from this perspective, the college degree is not a credential but an indirect measure of intelligence. People with college degrees tend to be smarter than people without them and, by extension, more valuable in the marketplace. Employers recruit at Stanford or Yale not because graduates of those schools know more than graduates of less prestigious schools but for the same generic reason that Willie Sutton gave for robbing banks. Places like Stanford and Yale are where you find the coin of cognitive talent.
Intelligence is fundamentally related to productivity. This relationship holds not only for highly skilled professions but for jobs across the spectrum. The power of the relationship is sufficient to give every business some incentive to use IQ as an important selection criterion.
1. Job training and job performance in many common occupations are well predicted by any broadly based test of intelligence, as compared to narrower tests more specifically targeted to the routines of the job. As a corollary: Narrower tests that predict well do so largely because they happen themselves to be correlated with tests of general cognitive ability.
2. Mental tests predict job performance largely via their loading on g.
3. The correlations between tested intelligence and job performance or training are higher than had been estimated prior to the 1980s. They are high enough to have economic consequences.
Why should it be that variation in general cognitive ability, g, is more important than job-specific skills and knowledge?
The really good busboy is engaged in using g when he is solving the problems of his job, and the more g he has, the more quickly he comes up with the solutions and can call on them when appropriate.
Job-specific items reveal mostly whether an applicant has ever been a busboy before. But that makes very little difference to job productivity, because a bright person can pick up the basic routine in the course of a few shifts. The g-loaded items, on the other hand, will reveal whether the applicant will ever become the kind of busboy who will clear table 12 before he clears table 20 because he relates the needed task to something that happened twenty minutes earlier regarding table 15. And that is why employers who want to select productive busboys should give applicants a test of general intelligence rather than a test of busboy skills. The kind of test that would pass muster with the courts—a test of job-specific skills—is a less effective kind of test to administer. What applies to busboys applies ever more powerfully as the jobs become more complex.
No comparable leveling-off effect has been observed for increasing intelligence. Wherever on the scale of intelligence pairs of applicants are, the smarter ones not only will outperform the others, on the average, but the benefit of having a score that is higher by a given amount is approximately the same throughout the range. Or, to put it more conservatively, no one has produced good evidence of diminishing returns to intelligence.”