Looking for Heteroscedasticity: A Means of Searching for Neglected Conditional Relationships in Political Communication Research.

Political communication researchers recently have emphasized conditional relationships as crucial to specifying and understanding the effects of the mass media. In many cases, however, researchers will not predict which variables will modify the form or existence of media effects. They therefore will not include measures of the conditional variables in research designs. The presence of heteroscedasticity, or unequal precision of prediction at different levels of an independent variable, suggests the likelihood of an overlooked conditional relationship. This paper examines the possibilities for the use of statistical tests of variation in mass communication research. Research situations that employ both discrete and continuous independent variables are covered, and the visual examination of scatterplots as an alternative to performing variability tests is examined. Problems with the variation tests available on commonly used computer packages is addressed. A number of recently developed, apparently dependable variability tests also are presented. A research example involving two-way, linear interactions is provided. Additional concerns with unequal variability are also discussed. Three figures and a four-page list of references are included. (Author/PN)