Methods of assessing effect size and the flows that limit their usefulness are discussed. The various statistical procedures for estimating variance accounted for are based on different statistical models producing sharply differing results. The methods reflect too greatly the particular study characteristics and hence have limited…

The central thesis of this article is that the process of eliminating validity threats depends fundamentally on no-difference findings, a fact that has not been made explicit by researchers. The implications of this neglect are explored using examples from a number of different substantive areas such as psychology, health, and medicine.…