This is a ranking of how often Democratic Senators vote with a majority of the Senate Democratic caucus. It factors every single vote that has been taken since the beginning of the current 113th session of Congress. All votes are weighted equally in this ranking, so a non-binding resolution honoring a collegiate sports team, for example, is considered equal to a vote on passing health care reform. Since the vast majority of the hundreds of votes factored in are routine in nature, the result is that even highly-independent senators have a seemingly high score on voting with their party. But it's the context that matters, and this ranking attempts to provide that. Obviously, this gives only a partial picture of the ideological spectrum. If you want to see how senators have voted on major legislation in Congress, check out our section of Hot Bills or use our head-to-head vote comparison tool to compare the voting records of any two members of Congress. The average Democrat -- Sen. Mark Udall [D, CO] -- votes with his party 95.0% of the time.