Nate Silver compares Ryan to past veeps:
Various statistical measures of Mr. Ryan peg him as being quite conservative. Based on his Congressional voting record, for instance, the statistical system DW-Nominate evaluates him as being roughly as conservative as Representative Michele Bachmann, the controversial congresswoman of Minnesota.
By this measure, in fact, which rates members of the House and Senate throughout different time periods on a common ideology scale, Mr. Ryan is the most conservative Republican member of Congress to be picked for the vice presidential slot since at least 1900. He is also more conservative than any Democratic nominee was liberal, meaning that is is the furthest from the center. (The statistic does not provide scores for governors and other vice presidential nominees who never served in Congress.)