Cook Partisan Voting Index

Map by state (After the 2016 election)

Map by 115th House district (After 2016 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]

Calculation

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. This is in contrast to the current system, where local elections are compared only to synchronic national ones.^[3] The change to an "apples-to-apples" comparison was the result of advocacy by David Nir of the Swing State Project.^[4]

Format

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

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 at R+33. As for states as a whole, Wyoming and Utah are the most Republican at R+25, and Hawaii is the most Democratic at D+18.

The most Democratic congressional district to be represented by a Republican is Florida's 26th with a PVI of D+6, represented by Carlos Curbelo. The most Republican congressional district to be represented by a Democrat is Minnesota's 7th with a PVI of R+12 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 2016 elections. The most Democratic-leaning state to have a Republican senator is Maine with Republican Susan Collins. The two least Republican-leaning states to have two Republican senators are Iowa, represented by Chuck Grassley and Joni Ernst, and North Carolina, represented by Richard Burr and Thom Tillis.

Three Republican-leaning states (the most Republican being Louisiana at R+11) have governors from the Democratic Party while twelve Democratic-leaning states (the most Democratic being Vermont at D+15) have governors from the Republican Party.

All Republican-leaning states have a majority Republican house delegation, as well as six Democratic-leaning states and two of the three neutral states: Pennsylvania and Wisconsin. The most Democratic-leaning state to have a majority Republican house delegation are Virginia, Michigan and Colorado at D+1, while the least Democratic-leaning state to have a majority Democratic delegation is Nevada which also has a PVI of D+1, and New Hampshire with a PVI of EVEN. 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). New Hampshire is also the only state with an EVEN PVI that has an entirely Democratic Delegation.

See also

• Psephology, the statistical analysis of elections.
• Political party strength in U.S. states

References

External links

• The Cook Political Report