What does it mean to have a high IQ? Well the first question to ask is “high IQ relative to whom?” Let us provide some background: relatives of modern-day IQ tests have been around since the late 1890s. The millions of test observations have enabled mathematicians and statisticians to establish several important characteristics about IQ scores. Namely, across a population, IQs follow a normal distribution which means that the same proportion of people will score higher than the average IQ score (usually set to 100), as the proportion of people scoring below the average score. In other words, 50% of the population have an IQ which is greater than 100, while the other 50% have an IQ lower than 100.
To be able to get a complete picture of the statistical properties of IQ however, you also need to know the standard deviation of the test that is being employed to measure the IQ score. The standard deviation measures the dispersion around the mean of all the test observations (scores) in your sample, or for the population. Most IQ tests have a standard deviation of either 15 or 16 (some tests such as Cattell have a standard deviation of 24).
A high IQ can be established by looking at statistical properties of the normal distribution
The beauty of the normal distribution is that once you know the mean (average) and the standard deviation, you can then calculate the percentile (and rarity) of a particular test observation or IQ score. Statistics tell us that about 68% of the population will have an IQ score which is 1 standard deviation (SD) away from the mean. So if the SD of a particular test is 15 for instance, we know that 68% of the population have an IQ between 85 and 115 (i.e. the mean of 100 + or – 15 SD points). About 95% of the population will have an IQ falling within 2 standard deviations of the mean. This means that 95% of people will score between 70 and 130 (again SD 15).
So from a statistical standpoint, you are comparing yourself to the average person (which is assumed to have an IQ score of 100) when you are interpreting your score. So let’s revisit the initial question of what a high IQ represents.
Given that the average score is 100, a high IQ will necessary start to the right of the distribution which is centred on the mean of 100. Most psychologists will agree that an IQ score between 90 and 109 falls withing the average category. A score of 110 to 119 is considered high average. 120-129 is superior intelligence, whilst IQs greater than 130 are considered very superior, a category which is something flatteringly referred to as ‘near genius’.
So we have seen that IQs between 110 and 119 are still considered to be high average. It is therefore not unreasonable to argue that a high IQ starts around 120.
The easiest ‘high IQ society’ to qualify for is Tensa, which requires a score in the top 10% or about 120. The International High IQ Society accepts a score in the top 5% (124 IQ with SD=15), while Mensa accepts applicants with an IQ score in the top 2% of the population (130 IQ if SD=15). Several other societies including the 999 society are much more selective, requiring a score in the top 99.9% to enter.
High IQ societies abound. But on a practical note, It is said that you can do virtually any job if you have an IQ of at least 115. So from a practical standpoint, a high IQ can be said to start at 115.
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