Experimental Effects

Abstract

The psychological literature has little to say about the constancy of experimental effects, whether those effects are the same for all individuals or vary with the individual. Investigators rarely specify whether the effects noted in research findings apply to every individual or are an average of varying individual effects. Where it does address the matter at all, namely in experimental design texts, the literature gives conflicting messages. It is argued here that a deterministic view of causation, which is implied in most propositions in psychology, leads to the expectation that effects are constant. The problems and confusion that result from viewing such effects as variable are explicated. The consequences of not addressing the issue of effect constancy are to leave statements of findings and propositions unacceptably vague and to encourage, in general, imprecise thinking about substantive matters.