Donald Campbell and his colleagues have elaborated an approach to research based on the elimination of threats to four validity types: internal, external, construct, and statistical conclusion. The central thesis of this article is that the process of eliminating validity threats depends...

How the magnitude of an experimental effect may be measured has been a matter of concern for at least two decades. The phenomenon of effect size is still not well under stood, and it cannot be inferred from statistical significance. In recent years various ways of assessing the amount of...

How the magnitude of an experimental effect may be measured has been a matter of concern for at least two decades. The phenomenon of effect size is still not well under stood, and it cannot be inferred from statistical significance. In recent years various ways of assessing the amount of...