My Campaign Desk item earlier today took issue with Tom Friedman’s argument that gerrymandered legislative districts are driving polarization in Congress, and cited a few political science papers that questioned that assumption. Here’s another one that finds only a modest relationship, Sean Theriault’s 2005 paper on “Party Polarization in Congress” (PDF):

Although both redistricting and the ideological migration and concentration of voters have polarized the parties, the biggest cause of party polarization has its roots within the institutions and procedures of the House and Senate; specifically, the manner in which roll call votes are structured and the issues being decided by those roll call votes. These changes, over the last 30 years, account for roughly half of the polarization in Congress.

Specifically, Theriault finds that together, redistricting and voter migration account for about one-fourth of the polarization in Congress. That’s not nothing, but it’s not going to usher in an era of blissful political consensus, either. And again, other studies find less of a relationship.

If you’ve got an Internet connection, this stuff is not hard to find—but you’ve got to be looking in the right place. In his column, Friedman attributed his ideas to Larry Diamond, whom he identified as “a Stanford University democracy expert.” As Diamond’s Hoover Institution bio page notes, though, his focus is on U.S. foreign policy and democratic development overseas. Given Friedman’s brief, it’s not surprising that Diamond is in his speed dial. But if you’re going to invoke an expert to talk about the causes of—and appropriate responses to—political polarization in the U.S., shouldn’t it be someone who has actually studied polarization in American politics?

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Greg Marx is an adjunct lecturer at The Medill School and a facilitator with The OpEd Project. She served as an editorial board member, columnist, library director, and No. 2 in the features department of the Chicago Sun-Times.