As a political scientist, it’s often frustrating to see Nate Silver being treated as an expert in the quantitative study of politics. Silver is obviously very bright, but he is a blogger who can run regressions and make charts, not a trained social scientist. As a result, while I like his energy and his quantitative approach, I typically find his analyses to be ad hoc and lacking any grounding in previous research.

Here’s a recent example. A few days ago, he wrote a post that compared the voting records of Senator Arlen Specter and Rep. Joe Sestak, who might challenge Specter in the 2010 Democratic Senate primary. To do so, Silver used the DW-NOMINATE scores developed by Keith Poole and Howard Rosenthal. Specifically, he compared the post-switch DW-NOMINATE score he projected (rather arbitrarily) for Specter with Sestak’s DW-NOMINATE score in the 110th Congress. The problem is that DW-NOMINATE scores are not comparable between chambers, which Silver would know if he had used them for research purposes. (Poole has developed other algorithms which generate scores that can be compared across chambers.) Even if you accept Silver’s questionable projection methodology, the whole exercise — which was cited by Josh Marshall — is simply invalid.

If you like Silver’s work and are interested in analytical blogging about politics, I would also recommend the work of top political scientist bloggers like Charles Franklin, Nolan McCarty, Andrew Gelman, and the folks at The Monkey Cage.