Measuring political polarization

Congress is more polarized than ever before. A National Journal study shows that, for the first time since the publication began tracking the divide 30 years ago, the most left-wing Republican is more conservative than the most right-wing Democrat. There is no overlapping set of moderates, who used to engineer congressional compromises. Here's an excerpt from the National Journal:

In the long march toward a more parliamentary and partisan Washington, National Journal’s 2010 congressional vote ratings mark a new peak of polarization.

For only the second time since 1982, when NJ began calculating the ratings in their current form, every Senate Democrat compiled a voting record more liberal than every Senate Republican—and every Senate Republican compiled a voting record more conservative than every Senate Democrat. Even Nebraska’s Ben Nelson, the most conservative Democrat in the rankings, produced an overall voting record slightly to the left of the most moderate Republicans last year: Ohio’s George Voinovich and Maine’s Susan Collins and Olympia Snowe. The Senate had been that divided only once before, in 1999.

But the overall level of congressional polarization last year was the highest the index has recorded, because the House was much more divided in 2010 than it was in 1999. Back then, more than half of the chamber’s members compiled voting records between the most liberal Republican and the most conservative Democrat. In 2010, however, the overlap between the parties in the House was less than in any previous index.