Nolan McCarty has come to my attention in recent years as a political scientist who does a lot of work that’s relevant to the field of political punditry — except he does it more accurately than a political scientist. As such, I’m a bit saddened to learn that he now has a blog since it used to be that those of us who’d read his book (with Keith Poole and Howard Rosenthal), Polarized America, had a competitive edge over the internet-only crowd.
At any rate, it promises to make interesting reading. Here’s a post examining the steady increase in the number of liberals, as measured by the DW-NOMINATE system, in the House of Representatives.
DW-NOMINATE scores, which are based on roll call voting records, run roughly from -1 to 1 where -1 is a very liberal score and 1 is a very conservative score. So to gauge how liberal a given House is, I simply compute the fraction of members with scores that fall beneath certain thresholds. The thresholds I chose were -.3, -.4, and -.5. To give the reader some context, Charlie Rangel and Nancy Pelosi score at approximately -.5, Rahm Emanuel clocked in just below -.4, and Dan Lipinski is just a little more liberal than -.3 (sorry that part of the ideological spectrum is devoid of household names).
The growth in the number of liberals reflects the fact that the Democratic Party has been growing stronger in recent cycles, but also the fact that the Democratic caucus that’s emerged since 1995 is a more liberal party than the old one which contained many conservative white southerners. | 
