The Cook Political Report, or the Cook Report for short, is the leading nonpartisan resource on likely election outcomes, redistricting, control of the House or U.S. Senate, and other future-looking political developments.
Charlie Cook founded it in 1984 after working as a staffer on Capitol Hill.
Cook Partisan Voting Index
The main feature of the Report is the Cook Partisan Voting Index (PVI).
There are actually two PVI's calculated: one for each state, and a separate for each Congressional district. The index is expressed as a letter (R for Republican, D for Democrat) followed by a plus sign and a number. The larger the number, the more likely that a state (or district) tends to vote for a particular political party.
Any state or district which voted within 0.5 percent of the national average is considered "Even".
The state calculation is based on the average of a state's voting in the two most recent Presidential elections, then compared to the national popular vote percentages. Similarly, the district calculation is based on the average of a district's voting in the same Presidential elections used for the state calculations, again compared to national percentages.
A detailed analysis of the ratings given by the Cook Report on election outcomes found that nearly 100% of the "Solid" category was correct, 95% of the "Likely" category proved right, and 85.7% of the "Lean" category became true. As to the "Toss Up" category, indeed about 49%-55% of of them were retained by the incumbent party.
- Although the District of Columbia is not a state nor does it have a Member of Congress, since it participates in Presidential elections due to the 23rd Amendment, a PVI is calculated for it as well.