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…

Assessment of 497 urban preschool children with developmental disabilities using the Vineland Adaptive Behavior Scales indicated a strong positive relationship between adaptive behavior and intelligence if measured globally. When Vineland domains were assessed separately, this relationship varied across domains and disability groups. With…

Relations among instruments used in community mental-health services for people with developmental disabilities were explored with 284 individuals. Correlation coefficients were evaluated for statistical significance and effect size for subtests of the Reiss Screen for Maladaptive Behavior, the Aberrant Behavior Checklist, and the Adaptive…