Cook Partisan Voting Index
The Cook Partisan Voting Index is a measurement of how strongly a United States congressional district or state leans toward the Democratic or Republican Party, compared to the nation as a whole. The index is updated after each election cycle. The Cook Political Report introduced the PVI in August 1997 to better gauge the competitiveness of each district using the 1992 and 1996 presidential elections as a baseline. The index is based on analysis by the Center for Voting and Democracy for its July 1997 Monopoly Politics report.
Calculation and format
PVIs are calculated by comparing a congressional district's average Democratic or Republican Party share of the two-party presidential vote in the past two presidential elections to the national average share for those elections. For example, the national average for 2004 and 2008 was 51.2% Democratic to 48.8% Republican. In Alaska's at-large congressional district, the Republican candidate won 63% and 61% of the two-party share in the 2004 and 2008 presidential elections, respectively. Comparing the average of these two district results against the average national share, this district voted 13.2 percentage points more Republican than the country as a whole, or R+13.Prior to its April 2009 update, the PVI formula compared district-level results for the past two presidential elections to nationwide results for only the most recent election. Since then, local elections are compared to synchronic national elections.
The Cook PVI is displayed as a letter, a plus sign, and a number. The letter reflects the major party toward which the district leans. The number reflects the strength of that partisan preference in rounded percentage points. A district or state without a partisan tilt is designated as "EVEN".
By congressional district
This table is sourced from the Cook Political Report's 2016 analysis for districts of the 116th United States Congress, calculated according to the results of the 2012 and the 2016 U.S. presidential elections. The party representations are based on the winners of the 2018 U.S. House elections. In the House, there are 235 districts that lean Republican and 192 districts that lean Democratic. The number of swing seats, defined as those between D+5 and R+5, is 73.The district-by-district list has been collapsed to save space. To show the full list, please click the word "show" in the table below.
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The District of Columbia's at-large congressional district is ranked on the Cook PVI, as it participates in presidential elections. It is represented by a non-voting delegate. Its rank is D+43. Territorial districts are not ranked on the Cook PVI, as they do not participate in presidential elections.
By state
The PVIs for states are calculated based on the 2012 and 2016 presidential election.Extremes and trends
The most Democratic congressional district in the country is New York's 15th, located in the Bronx, with a PVI of D+44. The most Republican district is Texas's 13th, based in the Texas Panhandle, at R+33. In terms of states as a whole, Wyoming is the most Republican at R+25, and Hawaii is the most Democratic at D+18.In the Senate, the most Republican-leaning state to have a Democratic senator is West Virginia, represented by Joe Manchin. The least Democratic-leaning state to have two Democratic senators is Michigan, represented by Debbie Stabenow and Gary Peters. The most Democratic-leaning state to have a Republican senator is Maine - with Susan Collins. The least Republican-leaning state to have two Republican senators is Florida, represented by Marco Rubio and Rick Scott.
Five states with a Republican-leaning PVI have Democratic governors, while four Democratic-leaning states have Republican governors. These governors are all seen as centrists who attracted voters from the opposite party. The most Republican-leaning state with a Democratic governor is Kentucky, with Andy Beshear, and the most Democratic-leaning state to have a Republican governor is Vermont, with Phil Scott. The two states with even PVI ratings, Pennsylvania and Wisconsin, both have Democratic governors.
In the House, the most Democratic-leaning congressional district represented by a Republican is New York's 24th; with a PVI of D+3, the district is represented by John Katko, who is also the only Republican to represent a Democratic-leaning House district. The most Republican-leaning congressional district represented by a Democrat is Utah's 4th; with a PVI of R+13, it is represented by Ben McAdams. Following the 2018 elections, there were 36 Republican-leaning House districts represented by Democrats. The only two Republican leaning states to have more Democratic house members than Republican house members are Iowa with 3 Democrats and 1 Republican, and Arizona with 5 Democrats and 4 Republicans. The most Democratic leaning state to have more Republican house members than Democratic house members is Wisconsin, with 5 Republicans and 3 Democrats. The most Democratic district relative to its state is Tennessee's 9th, being D+28 in an R+14 state. The most Republican relative to its state is Illinois's 15th, being R+21 in a D+7 state. The most Republican states to have a Democratic Representative are Oklahoma and Utah, while the most Democratic states to have a Republican Representative are California, Maryland, and New York. Of the 428 Congressional districts that are in states with more than one district, 104 lean to one party while their state leans to the other.