Experimental Validity: Brunswik, Campbell, Cronbach, and Enduring Issues

Abstract

Donald Campbell and Lee Cronbach had a long history of mutual respect for and fundamental disagreement with each other's ideas about experimental validity. Issues that Campbell labeled as external validity, Cronbach labeled internal validity. Issues that Campbell labeled internal validity, Cronbach suggested are trivial. Nevertheless, these methodological pioneers share much common ground, in part because of their alliance with Egon Brunswik. As science moved from a deterministic to a probabilistic paradigm, all 3 endeavored to protect behavioral science from validity-threatening practices that could result from naive use of the Fisherian approach to scientific investigation. This review shows that issues concerning the prioritization of types of validity still need to be resolved and that most social scientists do not understand internal validity. Several empirical practices for enhancing validity are suggested.