The Cook Partisan Voting Index (abbreviated CPVI or 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, based on how that district or state voted in the previous two Presidential elections.[a]
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 (now FairVote) 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 (62%) against the average national share (48.8%), 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.[better source needed]
The Cook PVI is displayed as a letter, a plus sign, and a number. The letter (either a D for Democratic or an R for Republican) reflects the major party toward which the district (or state) leans. The number reflects the strength of that partisan preference in rounded percentage points. A district or state that "performed within half a point of the national average in either direction" is designated as "EVEN".
By congressional district
The PVIs for congressional districts are calculated based on the 2016 and 2020 presidential elections. The party representations are based on the results for the most recent election in that district for the 117th Congress. The District of Columbia's at-large congressional district, represented by a non-voting delegate, is ranked by Cook PVI, as it participates in presidential elections – its PVI is D+43. Territorial districts are not ranked on the Cook PVI, as they do not participate in presidential elections.
As of 2021[update], in the House, there are 226 districts more Republican than the national average, and 203 districts more Democratic than the national average. Virginia's 2nd congressional district (R+1 PVI) was determined to be the median congressional district, meaning that exactly 217 districts are more Democratic and 217 are more Republican than this district. The number of swing seats, defined as those between D+5 and R+5, is 78.
|New Hampshire 1||R+1||Democratic|
|New Hampshire 2||D+1||Democratic|
|New Jersey 1||D+11||Democratic|
|New Jersey 2||R+4||Republican|
|New Jersey 3||R+3||Democratic|
|New Jersey 4||R+8||Republican|
|New Jersey 5||R+1||Democratic|
|New Jersey 6||D+6||Democratic|
|New Jersey 7||D+1||Democratic|
|New Jersey 8||D+24||Democratic|
|New Jersey 9||D+13||Democratic|
|New Jersey 10||D+34||Democratic|
|New Jersey 11||EVEN||Democratic|
|New Mexico 1||D+9||Democratic|
|New Mexico 2||R+8||Republican|
|New Mexico 3||D+7||Democratic|
|New York 1||R+6||Republican|
|New York 2||R+5||Republican|
|New York 3||D+3||Democratic|
|New York 4||D+4||Democratic|
|New York 5||D+34||Democratic|
|New York 6||D+13||Democratic|
|New York 7||D+34||Democratic|
|New York 8||D+33||Democratic|
|New York 9||D+32||Democratic|
|New York 10||D+27||Democratic|
|New York 11||R+7||Republican|
|New York 12||D+34||Democratic|
|New York 13||D+40||Democratic|
|New York 14||D+25||Democratic|
|New York 15||D+39||Democratic|
|New York 16||D+25||Democratic|
|New York 17||D+9||Democratic|
|New York 18||R+1||Democratic|
|New York 19||R+3||Democratic|
|New York 20||D+7||Democratic|
|New York 21||R+8||Republican|
|New York 22||R+9||Republican|
|New York 23||R+9||Republican|
|New York 24||D+2||Republican|
|New York 25||D+8||Democratic|
|New York 26||D+10||Democratic|
|New York 27||R+12||Republican|
|North Carolina 1||D+3||Democratic|
|North Carolina 2||D+12||Democratic|
|North Carolina 3||R+14||Republican|
|North Carolina 4||D+16||Democratic|
|North Carolina 5||R+20||Republican|
|North Carolina 6||D+10||Democratic|
|North Carolina 7||R+11||Republican|
|North Carolina 8||R+6||Republican|
|North Carolina 9||R+6||Republican|
|North Carolina 10||R+21||Republican|
|North Carolina 11||R+9||Republican|
|North Carolina 12||D+19||Democratic|
|North Carolina 13||R+20||Republican|
|North Dakota at-large||R+20||Republican|
|Rhode Island 1||D+12||Democratic|
|Rhode Island 2||D+4||Democratic|
|South Carolina 1||R+7||Republican|
|South Carolina 2||R+9||Republican|
|South Carolina 3||R+21||Republican|
|South Carolina 4||R+14||Republican|
|South Carolina 5||R+11||Republican|
|South Carolina 6||D+17||Democratic|
|South Carolina 7||R+11||Republican|
|South Dakota at-large||R+16||Republican|
|West Virginia 1||R+22||Republican|
|West Virginia 2||R+20||Republican|
|West Virginia 3||R+27||Republican|
The PVIs for states are calculated based on the results of the U.S. presidential elections in 2016 and 2020. The table below reflects the current state of Congress, based on the most recent election results, as of April 2021[update].
|New Jersey||D+6||Democratic||Democratic||10D, 2R|
|New Mexico||D+3||Democratic||Democratic||2D, 1R|
|New York||D+10||Democratic||Democratic||19D, 8R|
|North Carolina||R+3||Democratic||Republican||8R, 5D|
|South Carolina||R+8||Republican||Republican||6R, 1D|
* Includes an independent senator who caucuses with the Democrats.
Extremes and trends
The most Democratic congressional district in the country is Pennsylvania's 3rd, located in West Philadelphia, with a PVI of D+41. The most Republican district is Alabama's 4th, based in North Alabama, at R+34. In terms of states as a whole, Wyoming is the most Republican at R+26, and Hawaii and Vermont are the most Democratic at D+15.
In the Senate, the most Republican-leaning state to have a Democratic senator is West Virginia (R+23 PVI), represented by Joe Manchin. The least Democratic-leaning states to have two Democratic senators are Arizona (R+3 PVI), represented by Kyrsten Sinema and Mark Kelly, and Georgia (R+3 PVI), represented by Jon Ossoff and Raphael Warnock. The most Democratic-leaning state to have a Republican senator is Maine (D+1 PVI), represented by Susan Collins. The least Republican-leaning states to have two Republican senators are Florida (R+3 PVI), represented by Marco Rubio and Rick Scott, and North Carolina (R+3 PVI), represented by Richard Burr and Thom Tillis.
In the House, the most Democratic-leaning congressional district represented by a Republican is California's 21st (D+5 PVI), represented by David Valadao. The most Republican-leaning congressional district represented by a Democrat is Maine's 2nd (R+6 PVI), represented by Jared Golden. Following the 2020 elections, there were 28 Republican-leaning House districts represented by Democrats, and 7 Democrat-leaning House districts represented by Republicans.
- Political party strength in U.S. states
- Psephology, the statistical analysis of elections
- Two-party-preferred vote
- “Essentially, the Cook PVI uses national and state results from the last two presidential elections to calculate how each state leans relative to the country as a whole. For example, if a Democratic presidential candidate won the popular vote nationally by five points, he or she might win a D+2 state (which leans two points toward Democrats) by seven points. And if a Republican won the popular vote by three points, he or she might win a D+2 state by one point.” — D. Byler (2016)
- Cillizza, Chris (March 14, 2018). "The differences between real grassroots and 'Astroturf' matter". CNN. Retrieved November 29, 2020.
Which brings me to the Cook Political Report's Partisan Voting Index or PVI. The goal of the PVI is to compare every congressional district to every other congressional district based on how it has performed in each of the last two presidential elections.
- Benen, Steve (February 7, 2017). "There are 119 Republican House members who should be VERY nervous today". MSNBC. Retrieved November 29, 2020.
To get a sense of a congressional district's political leanings, there's a helpful metric called the Partisan Voter Index, or PVI, created 20 years ago by the Cook Political Report.
- Byler, David (October 7, 2016). "Trump trades traditional Republicans for swing-state voters". RealClearPolitics. Retrieved November 29, 2020.
- Wasserman, David (October 11, 2012). "Introducing the 2012 Cook Political Report Partisan Voter Index". The Cook Political Report. Archived from the original on May 4, 2013. Retrieved November 17, 2012.
- Wasserman, David; Flinn, Ally (April 15, 2021). "Introducing the 2021 Cook Political Report Partisan Voter Index". The Cook Political Report. Retrieved April 15, 2021.
- "Monopoly Politics". fairvote.org. Center for Voting and Democracy. July 1997. Retrieved November 17, 2012.
- "Partisan Voting Index Districts of the 113th Congress: 2004 & 2008" (PDF). The Cook Political Report. 2012. Archived from the original (PDF) on April 29, 2013. Retrieved November 29, 2020.
- Nir, David (February 6, 2009). "Swing State Project:: A Look at the Cook Political Report's Partisan Vote Index (PVI)". Swing State Project. Archived from the original on February 24, 2009. Retrieved August 5, 2017.