Keith Poole uses the NOMINATE program to turn roll call votes into ideal points. Simon Jackman uses some sort of Bayesian analysis to perform the same task. Usually, the two methods yield pretty similar results.
Yet Poole's approach finds that Russ Feingold of Wisconsin is the most liberal Democrat in the U.S. Senate, while Jackman's approach finds that Feingold is the fourth most conservative Democrat, sandwiched between McCaskill and Webb.
What's up with that?