Death to Dichotomizing

Abstract

Why call for a death to dichotomizing? The Journal of Consumer Research receives manuscripts on an almost daily basis in which researchers have dichotomized (often referred to as median splitting) a continuous independent variable. There are two principal problems with this approach to data analysis, each of which is very well documented in the literature. The first is that by dichotomizing continuous independent variables researchers are quite likely reducing the statistical power available to test their hypotheses (Irwin and McClelland 2003). The second, potentially more troubling, problem is that inappropriate dichotomizing of continuous data can at times create spurious significant results if the independent variables are correlated (Maxwell and Delaney 1993). And yet, despite these well-known problems, dichotomizing is an extremely frequent activity for experimental consumer researchers. The goal of this editorial is not to write an in-depth methodological piece on this subject but rather to briefly outline why all consumer researchers should be concerned about this topic. I also hope to illustrate how we can easily write up appropriately conducted analyses when our research designs include continuous independent variables. (For more thorough, methodological pieces on this topic I suggest an excellent and concise article in the Journal of Marketing Research [Irwin and McClelland 2001] or a truly comprehensive guide to performing analysis including continuous independent variables and interactions [Aiken and West 1991].)