This paper is directed to researchers who conduct and report education intervention studies. Its purpose is to stimulate and guide them to go a step beyond reporting the statistics that emerge from their analysis of the differences between experimental groups on the respective outcome variables. With what is often very minimal additional effort,…

This paper includes a nontechnical description of methods for calculating effect sizes in intellectual and developmental disability studies. Different hypothetical studies are used to illustrate how null hypothesis significance testing (NHST) and effect size findings can result in quite different outcomes and therefore conflicting results. Whereas…

Regression discontinuity designs (RDDs) are considered to be one of the strongest nonexperimental designs available for the purpose of identifying the effects of an intervention. RDD can be used in situations in which assignment to a treatment group is based on a cutoff value on a continuous assignment variable. The impact of the intervention is…