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How Are Scores on IQ Tests Calculated?


How Are Scores on IQ Tests Calculated?

The Normal Distribution of IQ Scores

Image courtesy Alessio Damato

Question: How Are Scores on IQ Tests Calculated?


We talk a lot about IQ scores, but the fact is that many people are not quite sure what these scores really mean. What exactly is a "high" IQ score? What is an average IQ? What kind of score does it take to be considered a genius?

In order to adequately assess and interpret test scores, psychometritians use a process known as standardization. The standardization process involves administering the test to a representative sample of the entire population that will eventually take the test. Each test taker completes the test under the same conditions as all other participants in the sample group. This process allows psychometricians to establish norms, or standards, by which individual scores can be compared.

Intelligence test scores typically follow what is known as a normal distribution, a bell-shaped curve in which the majority of scores lie near or around the average score. For example, the majority of scores (about 68%) on the WAIS-III tend to lie between plus 15 or minus 15 points from the average score of 100. As you look further toward the extreme ends of the distribution, scores tend to become less common. Very few individuals (approximately 0.2%) receive a score of more than 145 (indicating a very high IQ) or less than 55 (indicating a very low IQ) on the test.

What Is Considered a High IQ?

The following is a rough breakdown of various IQ score ranges. However, it is important to remember that IQ tests are only one measure of intelligence. Many experts suggest that other important elements contribute to intelligence, including social and emotional factors.

  • 115 to 129 - Above average; bright
  • 130 to 144 - Moderately gifted
  • 145 to 159 - Highly gifted
  • 160 to 179 - Exceptionally gifted
  • 180 and up - Profoundly gifted

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