Control of extraneous variables is a fundamental condition to causal interpretations of research (Johnson, 2001). Randomization of participants to treatment conditions has long been considered a powerful method of control, so much so that this is the distinguishing characteristic between true experimental and other types of research (Campbell & Stanley, 1963). When a researcher uses randomization, it is clear that the basis upon which participants receive treatment conditions is unrelated except by chance to any variable that can be confounded with the treatments.