Partisan Voter Index

Yesterday's post linked to data on presidential results in House districts. From the Cook Political Report:

The Cook Political Report is pleased to introduce the new 2014 Partisan Voter Index (PVI) for all 50 states and 435 Congressional districts in the country, compiled especially for the Report by POLIDATA®. First introduced in 1997, the Cook PVI measures how each district performs at the presidential level compared to the nation as a whole. In October 2012, we released new PVI scores for newly redrawn Congressional districts following redistricting. This release has updated our PVI scores to incorporate the results of the November 2012 presidential election.
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This year's Partisan Voter Index illustrates how voters' geographical self-sorting, even more than redistricting, has driven the polarization of districts over the last decade. The 2012 round of redistricting diminished the number of "Swing Seats" - those with PVI scores between R+5 and D+5 - from 103 to 99. But after the November 2012 election, the number of "Swing Seats" fell even more sharply, from 99 to 90. This means the number of competitive-range districts has fallen a total of 45 percent, from 164 to just 90, between 1998 and 2013.