Partisan Voting Index for the 2010 and 2012 US Elections
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Cook Partisan Voting Index or PVI is a measure of how strongly an American Congressional District or state leans toward one major political party or another compared with the United States as a whole. It was developed in 1997 by Charlie Cook of the Cook Political Report, a nonpartisan political newsletter, working with Polidata, a political statistics analysis firm.
The index for each Congressional District or state is derived by averaging the district or state voting results from the prior two presidential elections (the 2004 and 2008 elections, in this case) and comparing them to the latest winning national Presidential election results (Barack Obama's 52.9% in 2008, in this case). A Congressional District or state's index indicates which party's Presidential candidate was more successful in that district or state, as well as the number of percentage points by which that district or state's results exceeded the national average. The index is formatted as a letter ("D" for Democrat or "R" for Republican) + a number. For example, Colorado's 2nd Congressional District has a PVI score of D+11 during the 2010 US Congressional election because the two most recent Democratic Presidential candidates (John Kerry and Barack Obama) received an average of 11 percentage points more votes in the 2nd District than Barack Obama's aforementioned national average of 52.9% in 2008. Each PVI is rounded to the nearest whole number.
Please note that US Congressional districts were re-drawn for the 2012 Congressional election, based
on the results of the 2010 Census.