How can it be that IQ has such a huge deviation? I did the international IQ test 5 times in my life. The first result was 112, the second was 131, the third was 92, the fourth was 113, and the last was 129.

IQ tests, like all tests, are approximate measures of knowledge or ability. The score of 92 was an outlier since it was the only score that was below the “normed” average of 100, and was probably taken on a day when you were not functioning at your best. The scores of 112 and 113 are within one standard deviation from the average, while the scores of 129 and 131 hover around 2 standard deviations from the average. The best estimate of your IQ is probably around 120–124.

Mental performance, like physical performance varies from day to day. A golfer who wins a tournament one week, may perform abysmally in the following week. The statistical dispersion of scores on tests or in athletic competition varies even more significantly over long periods of time. If your IQ tests were taken over a span of 20 or more years, you can expect significant fluctuations in the results. All measures of a characteristic or skill are merely approximations of its true value.