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 2000 and 2004 elections, in this case) and
comparing them to the latest winning national Presidential election results (George W. Bush's 51.2% in 2004, 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 had a PVI score of D+8 during the 2008 election
because the two most recent Democratic Presidential candidates (Al Gore and John Kerry) received an average of 8 percentage points more
votes in the 2nd District than George W. Bush's aforementioned 51.2% in 2004. Each PVI is rounded to the nearest whole number.
Click here for a list of all members of the United States Congress (all United States Representatives and Senators listed
by State), with links to US Senators' information pages, as well as US Congressional Districts and their elected Representatives with
nationalatlas.gov US House District Maps and District-by-District Partisan Voting Indices. Links to Congressional office websites
included as well.
