How are intelligence quotient scores standardized?

Intelligence quotient scores are standardized by transforming raw test results into a normal distribution where the average score is set to 100. Modern tests use the deviation IQ method, which sets the standard deviation to 15 points, ensuring consistent definitions across both children and adults. Under this system, about two-thirds of the population scores between 85 and 115.

What we know

• For modern IQ tests, the raw score is transformed to a normal distribution with a mean of 100 and a standard deviation of 15. [3]
• An IQ score of 100 indicates performance equal to the average of the test-taker sample of about the same age used to norm the test. [2]
• About two-thirds of all test-takers obtain scores ranging from 85 to 115 under the standard deviation IQ method. [2, 3]
• The deviation IQ scoring method is used largely because it allows a consistent definition of IQ for both children and adults. [2]

Still open

• There is no universally employed standard naming or definition scheme for IQ score classifications across all test publishers.

Where to go next

• what followedWhat is the Flynn effect?
• how it workedHow was mental age used in early IQ tests?
• a case in pointWhat are the common classifications of IQ ranges?
• the bigger pictureHow does human intelligence get measured?
• whoWho were the early developers of IQ testing?
• an unexpected connectionHow do nutrition and socioeconomic status relate to IQ scores?IQ test scores, while standardized statistically, are found to be associated with concrete environmental factors like nutrition and parental socioeconomic status.

Sources

• [1]IQ classification (Wikidata Q5973340) · CC0 1.0
• [2]IQ classification · CC BY-SA 4.0
• [3]Intelligence quotient · CC BY-SA 4.0
• [4]IQ (disambiguation) · CC BY-SA 4.0
• [5]Flynn effect · CC BY-SA 4.0