In America, where there is a two-party system, there are numerous opportunities to compromise or cross party lines politically, so looking at where someone falls on a conservative-liberal graph lines doesn't tell us much about how they will vote. Democrats receive over 90 percent of education union donations, for example, so no left-right model predicted that the education reform known as No Child Left Behind would pass  91-8 in the Senate and 384-41 in the House.

Yet a Social Identity model might have, according to a new paper. The anti-vaccine, anti-food-science and anti-energy communities are overwhelmingly Democrats while the anti-climate-change community is overwhelmingly Republican, though both sides claim that not only do they accept science, but that it is on their side and that they are more pro-science than opponents. Social Identity reconciles those inconsistencies and it may predict how a member of Congress will vote. They say voting is not just friends and friends of friends, but also potentially something more subtle -- identifying with a movement without necessarily being part of an explicit "social circle." The weakness is the same that affects all social models - they predict the past but it is difficult to know if the scholars have created a tool that just maps cultural topology to existing data.

Writing in Research&Politics, the scholars sort legislators into ideological categories and analyzed the roll call votes of the 35th through 112th Congresses. They then reconstructed a voting record as essentially a weighted combination of "ideal voters" per politician's circles, which were discovered from the voting records that make up each Congressional session. They found that their new model is a much more accurate representation of the voting behavior by Senators and Representatives. The model was especially accurate in predicting Congressional voting in two periods - between 1876 and 1883, and in the 1970s and 1980s.

For example social identity voting shows that the Tea Party in the 112th House split essentially into two subgroups with issue-specific ideological differences on foreign policy and defense appropriations, so that the Tea Party is not an ideologically distinct faction of the Republican Party, it was instead a construct of the media. The success of in getting control of Congress for Democrats in 2006 was also just another flavor of Democrats catching a popularity wave with much greater success but was not a media focus and gets far less credit despite having more success - no one calls Elizabeth Warren a " candidate" the way media will label Tea Party Republicans, despite the fact that they have been her second-largest PAC.

Such group thinking may be why Senator Dianne Feinstein may claim to be for women but then create legislation that impacts hundreds of thousands of women who make their own soap and sell it.  A left-right axis can't predict that but social identity can, along with 

Says co-author Dan Rockmore, a professor of mathematics and computer science: "By focusing on group rather than individual preference, social identity voting gives a new way to look at and even uncover the forces driving Congress's voting behavior. Our approach sees political identity as derived from a range of group memberships, which are then expressed in the voting record."