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.^[1] This lower limit is known as the "floor".^[2] The "floor effect" is one type of scale attenuation effect;^[3] the other scale attenuation effect is the "ceiling effect". 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.^[4] 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^[5] 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.^[6]

• Ceiling effect (statistics)
• Bias (statistics)

• 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.
• 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.
• Groth-Marnat, Gary (2009). Handbook of Psychological Assessment (Fifth ed.). Hoboken (NJ): Wiley. ISBN 978-0-470-08358-1.