The problem with using a measure like an IQ score is that if the measure happens to work poorly for one particular person, the consequences can become very unbalanced. If IQ tests are more effective than other tests, but employers are banned from using IQ tests and have to use the less effective measures instead, their decisions will be more inaccurate. They will hire more poor workers, and more good workers will be unable to get jobs. But because the measures they do use vary from employer to employer, the effect on the workers will be distributed. If, say, an extra 10% of the good workers can't get jobs, that will manifest itself as different people unfairly unable to get jobs at different times--overall, the 10% will be distributed among the good applicants such that each one finds it somewhat harder to get a job, but eventually gets one after an increased length of jobless time. If the employers instead use IQ tests and can reduce this to 5%, that's great for them. The problem for the workers is that if IQ tests are poor indicators of performance for 5% of the people, that won't just be 5%, it'll be the same 5% over and over again. The total number of good-worker-man-years lost to the inaccuracy will be less with IQ tests (since IQ tests are more accurate), but the variance in the effect will be greater; instead of many workers finding it somewhat harder to get jobs, there'll be a few workers finding it a lot harder to get jobs. Having such a variance is a really bad thing. (Of course I made some simplifying assumptions. If IQ tests were permitted, probably not 100% of the employers would use them, but that would reduce the effect, not eliminate it. Also, note that this is a per-industry problem; if all insurance salesmen got IQ tested and nobody else, any prospective insurance salesman who doesn't do well at IQ tests relative to his intelligence would still find himself chronically unemployed.) The same, of course, applies to refusing to hire someone base