The standard deviation of IQ scores is 15 by definition. [That is, raw scores on the item content of IQ test batteries are generally not reported at all, but rather what is reported for each test-taker is a standard score defined as performance at the norming population median level being an IQ of 100, and performance one standard deviation up from that being an IQ of 115, and so on. All mainstream individual IQ tests have been scored this way for just about all of my lifetime.] P.S. I would take four standard deviations up or down [the IQ range of 40 to 160] as the outer limit of validated IQ scores, and indeed few modern IQ test batteries purport to report scores outside this range. See //en.wikipedia.org/wiki/IQ_classification and the published reference books cited there for more background. P.P.S. I should have mentioned when I first posted this comment that any IQ test has a standard error of measurement even if it is faultlessly administered and scored. Sometimes small-n studies like the study reported here have IQ score differences between two groups that are simply the result of the test errors showing a difference where no actual difference exists. IQ tests are often also very frequently administered incorrectly or scored incorrectly even if correctly administered, magnifying the size of the error band around the obtained score. For this study, I'm not sure if the human subjects tested were tested by test-givers who were "blind" to what group the test-takers were in, which could also be an issue. |
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By . Updated on May 21, 2019 What does an IQ score mean? What is the average IQ? 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. 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. Is your iq average? Do you have a genius IQ score? The table below shows an IQ scale chart that gives a clear overview of
the IQ score ranges as derived from Resing and Blok [2002]1. The table distinguishes different categories based on the height of your IQ score, meaning you gain some understanding of your capacities. It's not always easy to understand what IQ test scores mean. Most professional tests, like the culture fair intelligence test or the classical intelligence test, don't only give you a specific IQ score, they also mention an IQ range. This range shows you that your
score may vary within this IQ scale, due to error of measurement and because circumstances under which you take a test might be of influence. The average IQ score is always 100, and your personal score tells you your IQ ranking compared to that. IQ scores are based on comparisons with other people who took the test: the norm group. As 100 is the average score, your score tells you how your IQ score ranks compared to other people. There is no such thing as a 'normal iq range', although you
can distinguish categories like average intelligence [see the table at the top]. Most IQ classifications tend to take care in naming groups the distinguish. So, if you're looking to find what a genius IQ level is, 'very gifted' could be the phrase you are looking for. Want to know your IQ? Take one of our IQ tests. To the IQ tests 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.IQ score ranges
IQ scale
Interpretation of IQ score
% of population
above 130
Very gifted
2.1%
121-130
Gifted
6.4%
111-120
Above average intelligence
15.7%
90-110
Average intelligence
51.6%
80-89
Below average intelligence
15.7%
70-79
Cognitively impaired
6.4%
What does my IQ score mean?
Free IQ Test
The normal distribution
The IQ score chart below shows a visual representation and scale 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 17 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 classical IQ test and the culture fair intelligence test require a small fee but will give you a reliable and exact IQ score.
IQ score to percentile
Percentile to IQ score
Learn more on IQ scores and differences or take a free and short IQ test.
Recommended books on IQ and intelligence
- What Is Intelligence?: Beyond the Flynn Effect: Professor James Flynn is one of the most creative and influential psychologists in the field of intelligence. The 'Flynn Effect' refers to the massive increase in IQ test scores over the course of the twentieth century and the term was coined to recognize Professor Flynn's central role in measuring and analyzing these gains. Author: James R. Flynn
- The Curse of the High IQ: "Curse of the High IQ" is the first book specifically written for abnormally intelligent people. It identifies and addresses a litany of problems intelligent people face, as well as analyzes them and provides solutions. Author: Aaron Clarey
References
- 1 Resing, W.C.M., & Blok, J.B. [2002]. The classification of intelligence scores. Proposal for an unambiguous system. The psychologist, 37, 244-249.