Using Stata graphics as a method of understanding and presenting interaction effects

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.