Is it possible to have a negative IQ?

Answer 1

[Note: see arguments against the following answer below]

"No. A person's IQ (Intelligence Quotient) is a measure of their ability to solve logical problems and recognize visual-spatial relationships. In general, answering more questions correctly corresponds to a higher IQ, less correct answers mean a lower IQ, but even a person who answered no questions at all, or answered every question incorrectly, would still only be able to score as low as zero." -El Gordo

The above is actually completely wrong. The IQ system is set up as a standard distribution (bell curve) with 100 as the mean score, and a standard deviation of 15. To be negative you would have to be 6.7 standard deviations below the mean. This would be a profound state of mental retardation not necessarily recognizable on an IQ test, but then again once you reach a certain level of mental handicap (well above 0) you wouldn't be functional enough to understand the test at all. Nonetheless just because a special test would be required does not mean that you can't actually have a negative IQ, just as somebody with a super high IQ over 200 wouldn't be measurable by a standard test.

I initially wrote an answer disagreeing with the first response (that a negative IQ is impossible) and agreeing with the second. Theoretically, the IQ test could be designed so that if one scores enough standard deviations below the mean, their IQ would be negative. But I talked with my statistics professor today, who said that an IQ test's scores are fixed so that no one really will come up with a negative score. In other words, the researchers ensure that that won't happen.

Answer 2

No, IQ scores are designed so that the average score is set at 100, with a standard deviation of 15. Therefore, IQ scores cannot be negative.