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Princesses are bigger than Elephants: effect size as a category error in evidence based education

Simpson, A.

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Authors



Abstract

Much of the evidential basis for recent policy decisions is grounded in effect size: the standardised mean difference in outcome scores between a study's intervention and comparison groups. This is interpreted as measuring educational influence, importance or effectiveness of the intervention. This article shows this is a category error at two levels. At the individual study level, the intervention plays only a partial role in effect size, so treating effect size as a measure of the intervention is a mistake. At the meta‐analytic level, the assumptions needed for a valid comparison of the relative effectiveness of interventions on the basis of relative effect size are absurd. While effect size continues to have a role in research design, as a measure of the clarity of a study, policy makers should recognise the lack of a valid role for it in practical decision‐making.

Citation

Simpson, A. (2018). Princesses are bigger than Elephants: effect size as a category error in evidence based education. British Educational Research Journal, 44(5), 897-913. https://doi.org/10.1002/berj.3474

Journal Article Type Article
Acceptance Date Aug 21, 2018
Online Publication Date Sep 19, 2018
Publication Date Oct 1, 2018
Deposit Date Aug 22, 2018
Publicly Available Date Mar 19, 2020
Journal British Educational Research Journal
Print ISSN 0141-1926
Electronic ISSN 1469-3518
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 44
Issue 5
Pages 897-913
DOI https://doi.org/10.1002/berj.3474

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Copyright Statement
This is the accepted version of the following article: Simpson, A. (2018). Princesses are bigger than Elephants: effect size as a category error in evidence based education. British Educational Research Journal 44(5): 897-913, which has been published in final form at https://doi.org/10.1002/berj.3474. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.





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