Floor effect

In statistics, a floor effect (also known as a basement effect) arises when a data-gathering instrument has a lower limit to the data values it can reliably specify. This lower limit is known as the "floor".

Floor effects are occasionally encountered in psychological testing, when a test designed to estimate some psychological trait has a minimum standard score that may not distinguish some test-takers who differ in their responses on the test item content. Giving preschool children an IQ test designed for adults would likely show many of the test-takers with scores near the lowest standard score for adult test-takers (IQ 40 on most tests that were currently normed as of 2010). To indicate differences in current intellectual functioning among young children, IQ tests specifically for young children are developed, on which many test-takers can score well above the floor score. An IQ test designed to help assess intellectually disabled persons might intentionally be designed with easier item content and a lower floor score to better distinguish among individuals taking the test as part of an assessment process.

See also

Ceiling effect

Further reading

• Everitt, B.S. (2002) The Cambridge dictionary of Statistics, Second Edition. CUP. ISBN 0-521-81099-X
• Sternberg, Robert J., ed. (2000). Handbook of Intelligence. Cambridge: Cambridge University Press. p. 456. ISBN 978-0-521-59648-0. Lay summary (22 July 2013). 
• Weiss, Lawrence G.; Saklofske, Donald H.; Coalson, Diane; Raiford, Susan, eds. (2010). WAIS-IV Clinical Use and Interpretation: Scientist-Practitioner Perspectives. Practical Resources for the Mental Health Professional. Alan S. Kaufman (Foreword). Amsterdam: Academic Press. p. 8. ISBN 978-0-12-375035-8. Lay summary (16 August 2010). 
• Groth-Marnat, Gary (2009). Handbook of Psychological Assessment (Fifth ed.). Hoboken (NJ): Wiley. ISBN 978-0-470-08358-1. Lay summary (11 September 2010).