Tuesday, April 10, 2012

Biplots in Stata

I've been examining qualitative data using biplots, which are readily available in Stata using Ulrich Kohler's excellent package. For example, here is a biplot of a rich data set of poor white men on variables such as drug use and other risk factors:
There are several useful features of biplots: first, they concisely summarize a wealth of information in one graph, including relationships among both cases and variables; second, in line with Tufte's dictum, biplots have a high data-to-ink ratio; third, since cases are not directly modeled, biplots help with integrating qualitative and quantitative data (i.e., cases are not "hidden" by a hyperplane, as in a classical linear regression model); finally, there are absolutely no frequentist statistics to deceive the analyst.