Ron Paul is the outlier on the lower left.
The data points were generated by a technique called multi-dimensional scaling with relaxation, in which the high dimensional space of votes is projected into three dimensions for easy visualization.
The data indicate that Dems and Republicans do vote differently (duh!). Some people claim “there’s no difference between the Dems and the Repugs.” But the data, and common sense, indicate otherwise. That’s not to say that the Dems should escape accountability for their sellouts.
See too the