The Cook Partisan Voting Index, abbreviated Cook PVI, CPVI, or PVI, is a measurement of how strongly a United States congressional district or U.S. 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. The index is updated after each presidential election cycle, as well as after congressional redistricting. The Cook Political Report first 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 most recent iteration is the 2022 Cook Partisan Voting Index, which was released with an updated formula for calculating PVI values. Calculation and format 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". PVIs are calculated by comparing the lead candidate's average share of the two-party presidential vote in the past two presidential elections to the party's national average two-party share for those elections. In 2022, it was updated to weigh the most recent presidential election more heavily than the prior election. By congressional district The PVIs for congressional districts are calculated based on the 2016 and 2020 presidential elections. With a PVI of R+1, was determined to be the median congressional district, meaning that exactly 217 districts are more Democratic and 217 are more Republican than this district. , in the House, there are 222 districts more Republican than the national average, and 206 districts more Democratic than the national average. The number of swing seats, defined as those between D+5 and R+5, is 82. By state 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 and governors, based on the most recent election results. Extremes and trends The most Democratic district in the nation is , based in Oakland, with a PVI value of D+40. The most Republican district in the nation is (R+33), represented by Republican Robert Aderholt.