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…

The statistical method "meta-analysis" is perhaps unique as a contribution to empirical inquiry of many types because it arose entirely within the practice of education research. In spite of its origins, meta-analysis has found its widest application and most important contributions in the field of medicine. Contrasting the success of…

Using meta-analysis, randomized experiments in education that either clearly did or clearly did not experience student attrition were examined for the baseline comparability of groups. Results from 35 studies suggested that after attrition, the observed measures of baseline comparability of groups did not differ more than would be expected given…

During the 2009-2010 school year, Marzano Research Laboratory (MRL) was commissioned by Promethean Ltd. to conduct a second year evaluation study of the effects of Promethean ActivClassroom on student academic achievement. This report describes the findings from the second year study along with aggregate findings from the first and second year…

A review and meta-analysis were made of placebo control groups in educational experiments. In all, 125 studies were clustered into procedures that included (1) explicit manipulation of attentional elements; (2) explicit description of the placebo activity plus implied reference to attention; and (3) exclusive reference to the activity. (SLD)

A meta-analysis was conducted on 44 educational studies that used either a (labelled) Hawthorne control group, a manipulation of Hawthorne effects, or a group designed to control for the Hawthorne effect. The sample included published journal articles, ERIC documents or unpublished papers, and dissertations. The studies were coded on 20 variables,…

A descriptive analysis of research practices and a meta-analysis of control group effect sizes are used to address Hawthorne effects in educational experiments. The analysis of 86 studies and 256 treatment/Hawthorne/no-treatment control group effect size comparisons indicate that artifact controls have limited utility in dealing with the Hawthorne…