Some readers of the original piece questioned the usefulness of the data because they were unsure of how well Facebook political leanings represented the district’s political leanings. As an attempt to allay some of these concerns, we decided to see if there was any relationship between our score and other measures of political ideology.
The Cook Partisan Voting Index (PVI) is a measure of how strong a congressional district leans Democrat or Republican (for this exercise, we used 2014 numbers). While it does not directly measure political affiliation to broad ideological groupings, we believe that it could be used as a proxy, since the polarization of American politics placed almost all conservatives in the Republican Party and almost all liberals in the Democratic Party.
The numbers suggest a strong positive linear relationship between our score and the PVI (r = 0.84). While the relationship is clearly not perfect, it is reasonable to assume that Facebook political groupings are a somewhat mirror image of the district’s political learnings.