DW-NOMINATE is a method for analyzing data on preferences, such as voting data, developed by political scientists Keith T. Poole and Howard Rosenthal. Unlike the scoring done by interest groups, DW-NOMINATE doesn't rely on subjective determinations of what constitutes a liberal vote or a conservative vote--it sorts members of a population according to how similar each member's choices are to those of other members of the population. Two senators who vote the same way 90 percent of the time will be much closer to each other than two senators who only vote the same way 10 percent of the time. Poole and Rosenthal have used this method to discover some interesting statistics and trends going back to the First Congress in 1787-89.

Using House and Senate roll call votes as inputs, DW-NOMINATE has been used to chart every member of every Congress in a two-dimensional space. The primary dimension corresponds strongly to conventional notions of the liberal-conservative axis in modern politics, while the significance of the secondary axis tends to change over time (traditionally it tended to highlight the distance between Dixiecrats and the rest of the Democratic party; today it's kind of a more nebulous indicator of social and cultural differences and is, in my opinion, not particularly interesting). The point is that we can sort the members of a particular Congress by their scores on the primary dimension to easily rank them from most liberal to most conservative based entirely on their own voting data.

And when we do this for the period in which Hillary Clinton was in the Senate, here's what we get:



As it turns out, with a first-dimension score of -0.391 based upon her entire service in Congress, Hillary Clinton was the 11th most liberal member of the Senate in each of the 107th 109th , and 110th Congresses. That places her slightly to the left of Pat Leahy (-0.386), Barbara Mikulski (-0.385) and Dick Durbin (-0.385); clearly to the left of Joe Biden (-0.331) and Harry Reid (-0.289); and well to the left of moderate Democrats like Jon Tester (-0.230), Blanche Lincoln (-0.173), and Claire McCaskill (-0.154).

Some more numbers from the 110th Congress, to further help put things in perspective:





Most liberal Dem 1 Sanders -0.523

11 CLINTON -0.391

Median Dem 33 Biden -0.331

Most conservative Dem 51 B. Nelson -0.035

Most liberal Rep 52 Specter 0.061

Median Rep 76 McConnell 0.409

Most conservative Rep 101 Coburn 0.809



Oh, and a certain junior Senator from Illinois, Obama I think his name was? At -0.367, he ranked 23rd in the 110th Congress.

Comparing votes is hardly a perfect way to measure ideology, but it is by far the best method available to bring a measure of quantitative rigor to this inherently subjective topic, and political scientists and statisticians have long relied on DW-NOMINATE for insights about politics and voting behavior. (Nate Silver and FiveThirtyEight.com make extensive use of it to power their own results, for example.)

Like everyone else on Earth who does not wear my clothes and kiss my wife in the morning, Hillary Clinton disagrees with me on some things. The same is true for everyone here, and some of those differences may be profound. That is a conversation we can have. But suggestions that she is "a liberal republican or a conservative dem," to take one example of a quotation I read today, should stop here. By her voting record in Congress, Hillary Clinton is squarely in the mainstream of the national Democratic party in America, and would be a good ideological fit for it as its nominee. If anyone tries to tell you differently, ask them to show their work.