COOK PARTISAN VOTING INDEX

The 'Cook Partisan Voting Index (CPVI)', sometimes referred to as simply a 'Partisan Voting Index (PVI)', is a measure of how strongly an American congressional district leans toward one political party compared to the nation as a whole. It was originally developed in 1997 by the Cook Political Report, a nonpartisan political newsletter, working with Polidata, a political statistics analysis firm.
The index for each congressional district is derived by averaging the presidential election results in that district from the prior two elections, then comparing them to how the nation voted as a whole. The index indicates the more successful political party and how many percentage points higher than the national average for that party. It is published as a Letter + Number combination.

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Examples

Examples

A CPVI score of R+2 shows the Republicans received an average of 2 percentage points more votes than the national average. Likewise, a CPVI score of D+3 shows the Democrats received an average 3 percentage points more votes than the national average.