Introducing the 2017 Cook Political Report Partisan Voter Index

The Cook Political Report is pleased to introduce the 20th anniversary edition of the 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. We have released new PVI scores following every election since 1996 and every round of redistricting since 2001, each time taking into account the prior two presidential elections. This 2017 release has updated our PVI scores to incorporate the results of the November 2016 presidential election.

A Partisan Voting Index score of D+2, for example, means that in the 2012 and 2016 presidential elections, that district performed an average of two points more Democratic than the nation did as a whole, while an R+4 means the district performed four points more Republican than the national average. If a district performed within half a point of the national average in either direction, we assign it a score of EVEN.