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Encyclopedia of Autism Spectrum Disorders pp 1–2Cite as

Intelligence Quotient

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Synonyms

IQ

Definition

Intelligence quotient, abbreviated IQ, was originally the ratio of mental age to chronological age. The term “mental age,” popularized by early tests of intelligence, referred to the age of the children in the standardization sample whose performance the testee matched. Most tests of intelligence no longer use this ratio, and IQ instead refers to a person’s ability relative to available norms, which are usually age-based. By convention, IQ scores are designed to have a mean of 100 and a standard deviation of 15. Thus, about 95% of people fall within two standard deviations of the mean (i.e., 70–130). Norm-referenced scores have decreased reliability at extreme values; for this reason, most tests do not provide scores more than four standard deviations away from the mean (40–160). Giftedness is sometimes defined as scores more than two standard deviations above the mean. Intellectual disability is defined based on both IQ and adaptive behavior; however, the...

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References and Reading

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Author information

Authors and Affiliations

  1. National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA

    Cristan Farmer

Authors
  1. Cristan Farmer
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Corresponding author

Correspondence to Cristan Farmer .

Editor information

Editors and Affiliations

  1. Yale Child Study Center, New Haven, CT, USA

    Fred R. Volkmar

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© 2020 This is a U.S. Government work and not under copyright protection in the U.S.; foreign copyright protection may apply

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Farmer, C. (2020). Intelligence Quotient. In: Volkmar, F. (eds) Encyclopedia of Autism Spectrum Disorders. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-6435-8_1642-3

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  • DOI: https://doi.org/10.1007/978-1-4614-6435-8_1642-3

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  • Publisher Name: Springer, New York, NY

  • Print ISBN: 978-1-4614-6435-8

  • Online ISBN: 978-1-4614-6435-8

  • eBook Packages: Springer Reference Behavioral Science and PsychologyReference Module Humanities and Social SciencesReference Module Business, Economics and Social Sciences

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