Joanne Garrett () (Robert Wood Johnson Clinical Scholars Program, University of North Carolina at Chapel Hill)
Abstract
It is fairly simple to add an interaction term (also known as “effect modification” to epidemiologists) to a linear or logistic regression model, and test whether that term is statistically significant. However, it is much more difficult to explain what a significant interaction means in an intuitive way. A graphical representation of the interaction effect may help. Stata graphics can be used to give students a better understanding of what is actually happening when interaction is present. This can be helpful before introducing the mathematical approach and interpretation in a model. Graphing interactions also can be used as a simple method of exploratory data analysis, or for reporting final results in a non-statistical way in presentations or journal articles. Up-to-date versions of the programs may be obtained via ssc install predxcat and ssc install predxcon.
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