Can you statistically measure how “liberal” or “conservative” a member of Congress is? Can you even define those terms with language both side would accept?

Maybe. An academic review at the University of California-San Diego (where it’s now located; earlier versions of the project were elsewhere) has taken a stab at it with this review: Of “694 roll calls cast in the 110th House (not counting quorum calls). Of these, 485 had at least 0.5% or better in the minority and were used in the scaling. The rank ordering is based upon these 485 roll calls. Note that tied ranks are allowed.” The rankings probably shouldn’t be taken as gospel, but they are telling.

In the Senate, the regions’ four Democrats were well inside their caucus, with the two Oregonians (Ron Wyden and Jeff Merkley) ranking a little more liberal than the two Washingtonians (Patty Murray and Maria Cantwell). The Northwest’s two Republicans, Idaho’s Mike Crapo and Jim Risch, scored (almost identically) in about the middle of the Senate Republican caucus. In each case, about what you might expect.

Numerically, in the House, the rankings run from 1.0 for California Democratic Representative Bob Filner to 436.0 for Arizona Republican Representative John Shadegg. The two parties split nearly perfectly, with all Democrats (blue dogs included) scoring 257.0 or less, and all Republicans 258.0 or more – all, that is, but one.

Among Northwest Democrats, the most liberal was Washington’s Jim McDermott (23.0); among Republicans, the most conservative was Oregon’s Greg Walden (349.0).

But here’s the stunner: The most “conservative” member of the Northwest delegation turns out not to be a Republican at all, not Idaho’s Mike Simpson (281.0) or Washington’s Dave Reichert (263.0), Doc Hastings (312.0) or Cathy McMorris-Rodgers (341.5).

Rather, it is the only Democrat in the House to score more conservative than the “least conservative” Republican – Idaho’s Walt Minnick, at 359.5, which puts him just about in the middle of the House Republican caucus, and more “conservative” than, for example, Simpson. No other Democrat or Republican scores across the line at all.

UPDATE Minnick’s office has taken a look at the numbers, and emailed us a comment on them:

First, it’s no secret that Walt has the most independent voting record in Congress. Not “one of the most” but THE most, according to CQ and the Washington Post. [Editor: The chart makes that point pretty conclusively.] He is already more “conservative” (if that’s the word you choose to use) than any other member of his caucus. And this data shows he is more conservative than some members of the other party, which I think is reflective of the District.

All that said, we were surprised by the raw numbers you linked to — until we looked at the data. I can explain most of the disparity with two words: Jeff Flake. Flake is a GOP representative from Arizona who has made it his personal crusade this session of Congress to introduce hundreds of amendments to strip earmarks from appropriations bills. Many of those amendments ultimately make it to the floor. The vast majority of Republicans and almost all of the Democrats vote against those amendments. However, Walt has joined a handful of folks who refuse earmarks to vote with Flake, on principle, for each amendment.

Our legislative director looked at the data this morning for me, and confirmed that Flake’s amendments and similar anti-earmark votes are the cause of the disparity.