Nate Silver displays Newt Gingrich's unimpeachable conservative credential

Nate Silver used the pictoral depiction of data to point out Newt Gingrich's one unimpeachable conservative credential:

The chart below shows the DW-Nominate score for the median member of the House of Representatives dating back to the 1930s. DW-Nominate is a statistical system that evaluates the liberalness or conservatism of a member of Congress on economic policy based on his voting record. Positive scores indicate a more conservative member and negative scores a more liberal one. I have portrayed these as moving in the intuitive direction from left (liberal) to right (conservative) in the chart.




The two large red circles in the chart represent the 104th and 105th Congresses, during which Mr. Gingrich was the Speaker of the House. As you can see, they were associated with an extremely large conservative shift. Part of this is because Republicans had gained 53 seats at the preceding midterm elections and so represented the swing votes in the chamber. But the newly elected Republicans also tended to be quite disciplined in their conservative voting even if they came from moderate districts. The typical Republican member of Congress was more conservative in the 104th Congress than in the 103rd Congress, something that traditionally had not happened when a party does well at an election and expands its coalition.

In other words, Newt not only took the house from the Democratic Party, which had controlled it for 42 years, but he managed to break the New Deal Coalition as the ruling force (the current Democratic Party is not the New Deal Coalition, if for no other reason than that the Dixiecrats have all left to become Republican and a lot of socially liberal Northern Republicans have become Democrats, myself among them), and move the House farther to the right than it had been been since 1931. Then he was able to move the House even farther right. That's quite the conservative credential.

Nate, however, didn't color the dots properly, as I noted in a comment:

I have only one complaint; shouldn't the dots for the median U.S. House member elected in 2006 and 2008 be blue? Other than that, it's a very good graph. Not only does it show the massive swing of the median U.S. House member from moderately liberal to moderately conservative after 1994, but it also shows how the House became steadily more conservative over time with a Republican majority, a trend not broken by the four years of Democratic majority. The current U.S. House may be markedly more conservative than its predecessor, but its ideological location is exactly where one would have predicted it would be if the trend from 1998 through 2004 had continued uninterrupted. If anyone wants to see the rightward swing of the GOP, it's right there.

It turns out that Nate had forgotten to color two other dots correctly, either. The GOP also controlled the U.S. House in 1947-1949 (this was the "Do Nothing Congress" Truman campaigned against) and 1953-1955, both of which were led by Speaker Joseph William Martin, Jr. Those dots should also be colored red. If you look for them, they're the two dots farthest to the right in the upper half of the graph--by not very much. Back then, the GOP was a lot less conservative than it is now and the Democrats were less liberal.

Speaking of which, note the trend of the Democratic-controlled Houses from 1985-1993, then look at the positions of the 2007 and 2009 Houses. Just like the current House fits on the trend established by the earlier GOP majorities, the previous two House continues the trend established by the pre-1994 Democratic majorities. Both parties are moving away from the center, although the GOP is moving farther and faster.