Adrian Simpson
Princesses are bigger than elephants: Effect size as a category error in evidence?based education
Durham University
much evidential basis recent policy decisions grounded effect size standardised mean difference outcome scores studys intervention comparison groups interpreted measuring educational influence importance effectiveness intervention article shows category error two levels individual study level intervention plays partial role effect size treating effect size measure intervention mistake metaanalytic level assumptions needed valid comparison relative effectiveness interventions basis relative effect size absurd effect size continues role research design measure clarity study policy makers recognise lack valid role practical decisionmaking