Theory and External Validity

Winer (1999 [this issue]) proposes that external validity concerns require more attention in theoretical research. The author argues that one cannot “enhance” external validity by choosing one method over another. External validity can only be “assessed” by better understanding how the focal variables in one’s theory interact with moderator variables that are seen as irrelevant early in a research stream. Findings from single real-world settings and specific sets of “real” people are no more likely to generalize than are findings from single laboratory settings with student subjects. Both the laboratory and real world vary in background facets of subject characteristics, setting, context, relevant “history,” and time. It is only when these facets vary and we see how they interact that understanding of external validity is enhanced. For this to happen, the observable “background” factors have to be conceptualized in terms of more general constructs and incorporated as moderators into the researcher’s theory. Enriched theory— not method—confers confidence in our understanding of whether effects will be robust or highly contingent. To map this knowledge to some specific substantive system requires an added step of understanding the mapping from observables in that system onto theoretical constructs. The author proposes “friendly amendments” to Winer’s three proposals to pursue a better understanding of external validity through theory.