How does the Cook Partisan Voting Index classify each state and what does D+ or R+ mean?
Executive summary
The Cook Partisan Voting Index (Cook PVI) rates every U.S. state and congressional district by how much more Democratic or Republican it voted in the last two redistricting-in-the-united-states">presidential elections compared with the national average; each state receives a label such as D+4, R+7 or EVEN that quantifies that lean in percentage points [1] [2]. The index is updated after each presidential cycle and redistricting, uses presidential returns to allow cross‑state comparison, and since the 2020 cycle has shifted its formula to weight the more recent election more heavily [3] [4].
1. What the letters and numbers mean: a straight translation
A Cook PVI expressed as D+X or R+X means that a state or district voted X percentage points more Democratic (D+X) or Republican (R+X) than the nation’s two‑party presidential vote average over the measured elections; a score of EVEN means it voted within about half a point of the national average [1] [5]. For example, D+2 indicates roughly a two‑point Democratic advantage relative to the nationwide presidential two‑party vote, while R+4 indicates roughly a four‑point Republican advantage [1] [6].
2. How Cook actually calculates those numbers
Cook compares the two‑party presidential vote share in each state or district to the national two‑party result across the two most recent presidential elections; the resulting difference is the PVI [3] [1]. Beginning in the 2020/2022 recalculation, Cook altered the formula to weight the more recent presidential result more heavily (a 75/25 weighting in favor of the latest election rather than a strict 50/50 mix), a tweak Cook says makes recent electoral shifts more visible [4] [7].
3. How states are classified and where to find the state list
Every state receives a numeric PVI and an orientation (D or R); Cook publishes full state maps and lists after each presidential cycle and after redistricting so users can see which states "lean" Democratic, which "lean" Republican, and which are effectively even [2] [7]. The 2025 Cook PVI release and the Cook Political Report’s state map list contain those state‑level ratings and are the canonical source for current state classifications [6] [2].
4. What classifications imply — and what they do not
A PVI is a measure of partisan baseline, not a forecast: it describes past presidential performance relative to the nation and is intended to reflect "underlying partisanship," not to predict every race or capture local dynamics like candidate quality, turnout anomalies, or non‑presidential contests [1]. Cook itself distinguishes PVI from race ratings, which incorporate campaign‑specific factors to predict outcomes [1]. Users should also note that PVI relies solely on presidential results to allow cross‑state comparability, which is both its strength and a limitation [3].
5. Known caveats, methodological debates and redistricting effects
Scholars and practitioners note that relying on presidential returns sidesteps the comparability problems of other offices but creates challenges when redistricting changes boundaries or when aggregation practices differ by state; Cook and third‑party observers have flagged inconsistencies and the need to adjust methodology after redistricting cycles [3] [5]. Additionally, changes like Cook’s 75/25 weighting reflect an implicit judgment that recent elections better predict future partisan lean — a defensible but judgmental choice that can shift a state's label without a dramatic on‑the‑ground change [4] [7].
6. Bottom line for interpreting D+ and R+ labels
D+ or R+ labels are shorthand: they quantify how many percentage points a place has leaned more Democratic or Republican than the U.S. as a whole in the measured presidential cycles, provide a consistent cross‑jurisdictional baseline for comparison, and are updated by Cook after each presidential election and redistricting cycle; however, they are not all‑purpose predictors and must be read alongside local factors, updated maps, and Cook’s methodological notes [1] [2] [3].