Cook Partisan Voting Index

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Map by state (After the 2012 election)

The Cook Partisan Voting Index, also called PVI, 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 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.[1] The index is based on analysis by the Center for Voting and Democracy (now FairVote) for its July 1997 Monopoly Politics report.[2]


PVIs are calculated by comparing the district's average Democratic or Republican Party's share of the two-party presidential vote in the past two presidential elections to the nation's average share of the same. The national average for 2004 and 2008 was 51.2% Democratic to 48.8% Republican.[1] For example, 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 results (62%) against the average national share (49%), this district has voted 13 percentage points more Republican than the country as a whole, or R+13.

Prior to its April 2009 update, the PVI formula was calculated by comparing district-level results for the past two presidential elections to nationwide results for the most recent election. David Nir of the Swing State Project advocated a change to the new formula, and Charlie Cook agreed, wanting an "apples to apples" comparison.[3]


The Cook PVI is formatted as a letter, plus sign, and number:

  • Letter: The major party, Democratic (D) or Republican (R), to which the district leans
  • Number: The extent of that lean, in rounded percentage points

For districts without a lean, the index written as "EVEN" without a number.

List of PVIs[edit]

Extremes and trends[edit]

The most Democratic congressional district in the country is New York's 15th, located in the Bronx, with a PVI of D+43. The most Republican district is Texas's 13th at R+32. As for states as a whole, Wyoming and Utah are the most Republican at R+22, and Hawaii is the most Democratic at D+20.

The most Democratic congressional districts to be represented by a Republican are Iowa's 1st and New York's 24th with a PVI of D+5. Iowa's 1st is represented by Rod Blum and New York's 24th is represented by John Katko. The most Republican congressional district to be represented by a Democrat is Minnesota's 7th and it is represented by Collin Peterson. In total there are nine Democratic-leaning House districts represented by Republicans following the 2014 elections (up from five from before the election) and eight Republican-leaning House districts represented by Democrats (down from 15 before the election). This represents a total of 17 out of 435 Representatives from districts with a PVI opposite to their own party.

In the Senate, the most Republican-leaning state to have a Democratic senator is West Virginia, with Democrat Joe Manchin. The least Democratic-leaning state to have two Democratic senators is Virginia, represented by Mark Warner and Tim Kaine, with no Republican-leaning states at all having elected two Democrats as of the 2014 elections. The most Democratic-leaning state to have a Republican senator is Maine with Republican Susan Collins. The most Democratic-leaning state to have two Republican senators is Iowa, represented by Chuck Grassley and Joni Ernst.

Four Republican-leaning states (the most Republican being West Virginia at R+13) have governors from the Democratic Party while twelve Democratic-leaning states (the most Democratic being Vermont at D+16) have governors from the Republican Party.

All Republican-leaning states have a majority Republican house delegation, as well as six Democratic-leaning states and neutral Virginia. The most Democratic-leaning state to have a majority Republican house delegation is Michigan at D+4, while the least Democratic-leaning state to have a majority Democratic delegation is New Hampshire at D+1. Massachusetts has the largest number of Representatives (nine) of the six states that have entirely Democratic delegations; Oklahoma has the largest number of Representatives (five) of the eleven states that have entirely Republican delegations. Note that the seven states with only one representative must be among these; two are Democratic (Delaware and Vermont) and five are Republican (Wyoming, South Dakota, North Dakota, Montana, and Alaska).

See also[edit]


  1. ^ a b c Wasserman, David (October 11, 2012). "House About PVI". The Cook Political Report. Retrieved November 17, 2012. 
  2. ^ "Monopoly Politics". Center for Voting and Democracy. July 1997. Retrieved November 17, 2012. 
  3. ^ "Cook Releases 2008 PVIs, With a Change SSPers Will Like". Swing State Project. April 9, 2009. Retrieved November 17, 2012. 
  4. ^ "Partisan Voting Index, Districts of the 113th Congress" (PDF). The Cook Political Report. Retrieved September 23, 2014. 
  5. ^ "Partisan Voter Index by State, 1994–2014" (PDF). The Cook Political Report. 2013. Retrieved December 23, 2014. 

External links[edit]