Confirmatory Methods, or Huge Samples, Are Required to Obtain Power for the Evaluation of Theories

Abstract

Experimental studies are usually designed with specific expectations about the results in mind. However, most researchers apply some form of omnibus test to test for any differences, with follow up tests like pairwise comparisons or simple effects analyses for further investigation of the effects. The power to find full support for the theory with such an exploratory approach which is usually based on multiple testing is, however, rather disappointing. With the simulations in this paper we showed that many of the common choices in hypothesis testing led to a severely under-powered form of theory evaluation. Furthermore, some less commonly used approaches were presented and a comparison of results in terms of power to find support for the theory was made. We concluded that confirmatory methods are required in the context of theory evaluation and that the scientific literature would benefit from a clearer distinction between confirmatory and exploratory findings. Also, we emphasis the importance of reporting all tests, significant or not, including the appropriate sample statistics like means and standard deviations. Another recommendation is related to the fact that researchers, when they discuss the conclusions of their own study, seem to underestimate the role of sampling variability. The execution of more replication studies in combination with proper reporting of all results provides insight in between study variability and the amount of chance findings.