IQ tests have been in widespread use since World War One, when the US Army employed them to determine the aptitude of draftees and recruits. The tests are regularly "renormalized" so that the average score is always 100.
We all have heard people toss around their supposed results, and they always are phenomenally high.
"Mine is 142."
"Oh yeah, mine is 156."
All of these are very unlikely numbers, regardless of what scale is being used, but one should remember there is more than one scale. There are several well-known publishers of tests and many lesser known ones. Scorers fit the raw results of tests into a bell curve. The most common one has a standard deviation of 15, so that half the population falls between 85 and 115. Only 2% score above 130 on this scale. Scores of 140 or higher are truly rare. Some tests have standard deviations of 16 or 24. These are not preferred by most professionals, but they are very popular with test–takers who are just on the high side of average. After all, a test result of 124 simply looks better than one of 115, even though both may mean the exactly same thing when different scales are taken into account – and of course we’ll add the same number to this figure as the pounds we subtract from our weight when we mention the results in company. Tests typically found in magazines or on the net produce wildly exaggerated results in order to flatter subscribers, and ought not to be taken seriously.
IQ tests do tell us something, but they need to be treated with caution and skepticism. It is well to remember that motivated 95s often outperform lazy 125s academically and in life. High scores are no guarantee of happiness either. In Voltaire’s The Story of a Good Brahman, a Brahman and his intellectual friends conclude after much discussion that happiness is the proper goal in life. Yet, faced with proof that an ignorant cleaning woman is cheerier than any of them, none says he would opt to trade brains for happiness. Voltaire ends there and doesn't try to resolve the contradiction.