Analysis of Pre‐test‐Post‐test Control Group Designs in Educational Research

Abstract

Pre‐test‐post‐test control group designs are well suited to investigating effects of educational innovations and are common in educational research. They are frequently analysed by means of an ANOVA on change scores, or, what amounts to the same thing, a repeated measures ANOVA to test the treatment by occasion interaction. Although the analysis of change scores has intuitive appeal, such analyses are often inappropriate. An ANCOVA on post‐test scores, with pre‐test scores as co‐variate usually provides a more appropriate and informative analysis. Advantages of the ANCOVA approach are explained and illustrated using SPSS‐X analyses of fabricated data sets.