Meaning of an IQ score
What does an IQ score mean? After taking an IQ test, you might need some help with the interpretation of your IQ score to understand what your IQ score actually tells you. Do you have an average IQ, a genius IQ? The table below shows the IQ score range as derived from Resing and Blok (2002)1 and provides a clear overview. The table distinguishes different categories based on the height of your IQ score, meaning you gain some understanding of your capacities.
|IQ||Percentage of the population with this IQ||Interpretation|
|> 130||2.1||Very gifted|
|111-120||15.7||Above average intelligence|
|80-89||15.7||Below average intelligence|
About 2% of the population has an IQ score lower than 69. Such a low IQ score often is hard to measure using a regular intelligence test. Very high IQ scores are also hard to determine accurately. This is because you need a lot of reference measurements to determine a specific score reliably. As very high and very low IQ scores simply do not occur often, it is hard to form such a reference group.
The normal distribution
Although the IQ score is widely known as a psychological statistic, its relation to other statistical measures is lesser known. The best way to explain these measures and their relations is using the normal distribution, also know as the Bell Curve.
The IQ score chart below shows a visual representation of a normal distribution. Think of the horizontal axis as all the different scores one could possibly get, lowest through highest. The vertical axis represents the number of people that obtain that specific score.
An IQ test score is calculated based on a norm group with an average score of 100 and a standard deviation of 15. The standard deviation is a measure of spread, in this case of IQ scores. A standard devation of 15 means 68% of the norm group has scored between 85 (100 – 15) and 115 (100 + 15). In other words, 68% of the norm group has a score within one standard deviation of the average (100).
Also, 95% of the norm group has an IQ score within two standard deviations of the average. So, 95% of the norm group has a score between 70 (100 – 30) and 130 (100 + 30). This means scores of over 130 only occur in 2,5% of cases. For example, the Netherlands has 16 million inhabitants. Based on chance, only 25 of these inhabitants would have an IQ score of 170. There would only be one person with an IQ score of 180. Only 4 out of 1000 would score at least 140 on an IQ test. A lot of online tests score you 130 or higher relatively easy. These tests often have a different goal, like collecting information for marketing purposes. The IQ test at IQ-test.com requires a small fee but will give you a reliable and exact IQ score.
1Resing, W.C.M., & Blok, J.B. (2002). The classification of intelligence scores. Proposal for an unambiguous system. The psychologist, 37, 244-249.