Cook Partisan Voting Index

Cook Partisan Voting Index
Name	Cook Partisan Voting Index
Acronym	CPVI
Introduced	1997
Publisher	The Cook Political Report
Founder	Charlie Cook
Purpose	Measure of partisan lean of United States congressional districts and U.S. states
Latest update	2022

Cook Partisan Voting Index

The Cook Partisan Voting Index provides a comparative measure of how strongly a United States congressional district or U.S. state leans toward the Democratic Party or the Republican Party relative to national presidential vote averages, used by analysts such as Charlie Cook, Amy Walter, and contributors at The Cook Political Report. It is widely cited by observers including journalists at The New York Times, The Washington Post, and television networks like CNN and Fox News Channel when assessing competitiveness in midterm and presidential elections. Political strategists from organizations such as Democratic Congressional Campaign Committee, National Republican Congressional Committee, think tanks like the Brookings Institution, and academics at institutions like Harvard University and Stanford University use the index alongside polling from firms such as Gallup and Pew Research Center.

Overview

The index quantifies partisan lean by comparing the two-party share of the last two United States presidential election votes in a district or state to the national two-party presidential vote. Analysts at The Cook Political Report publish ratings each cycle that inform campaign decisions by actors including candidates endorsed by Emily's List, committees such as Club for Growth, and labor unions like the AFL–CIO. Media outlets including Associated Press, Reuters, and Politico routinely display CPVI alongside metrics from FiveThirtyEight, RealClearPolitics, and academic measures from scholars at Columbia University and Yale University.

Methodology

The CPVI calculation uses results from the two most recent United States presidential elections to compute an average two-party vote share for each district or state, then subtracts the national average two-party share for that period. The Cook Political Report adjusts for redistricting performed by bodies such as state legislatures in Texas, California, and North Carolina and court decisions like those from the Supreme Court of the United States or state supreme courts. The index is recalculated after reapportionment and redistricting cycles influenced by the United States Census and reapportionment law. Data sources include official results certified by state secretaries of state in jurisdictions such as Florida, Ohio, and Arizona and datasets maintained by scholars at MIT Election Data and Science Lab and the Inter-University Consortium for Political and Social Research.

Historical Trends and Changes

Since its introduction in 1997 by Charlie Cook and colleagues, the CPVI has reflected major partisan realignments surrounding events such as the Clinton administrations, the Bush administration, the aftermath of the 2008 election with Barack Obama, the 2016 election of Donald Trump, and the polarized contests of the 2020 election. Shifts in suburban voting patterns in metropolitan regions like Atlanta, Charlotte, Philadelphia, Phoenix, and Houston produced notable CPVI swings, while rural districts in states including Iowa, Wisconsin, and Michigan showed opposite trends. Redistricting after the 2010 census and 2020 census produced structural changes that analysts compared with historical measures from scholars at Princeton University and forecasting models by Nate Silver.

Applications and Influence

Campaign managers for candidates like those supported by MoveOn, Heritage Action for America, and Human Rights Campaign use CPVI to allocate resources and design field strategies, often alongside fundraising data from the Federal Election Commission and voter files maintained by state parties such as the California Democratic Party and the Republican National Committee. Journalists at outlets such as NBC News, CBS News, and Bloomberg News use CPVI to contextualize special elections and retirements from members of the United States House of Representatives and United States Senate. Political scientists at institutions like Duke University and University of Michigan incorporate CPVI into studies of incumbency advantage, polarization, and electoral volatility, comparing it with metrics like the Gerrymandering index and measures used by the Brennan Center for Justice.

Criticisms and Limitations

Critics including academics at Boston University and watchdogs such as Brennan Center for Justice note CPVI’s reliance on presidential elections may not capture down-ballot dynamics for figures like Senator Joe Manchin, Representative Alexandria Ocasio-Cortez, or local officials in cities such as New York City and Los Angeles. The index’s two-election averaging window can lag during rapid realignments triggered by events like the Great Recession or the COVID-19 pandemic. Analytic limitations are raised by scholars at University of Chicago who argue that CPVI ignores turnout differentials emphasized in research by Michael McDonald and voter mobilization efforts by groups like Priorities USA Action and American Crossroads. Critics also point to complications when applying CPVI in states with top-two primary systems like California or ranked-choice voting pilots in jurisdictions such as Maine.

Notable Examples and Records

Some districts have extreme CPVI ratings reflecting entrenched partisan voting: historically lopsided districts include seats in states such as Massachusetts and Alabama held by long-serving members like those formerly represented by figures reminiscent of John Lewis or William Lacy Clay. Competitive swing districts with narrow CPVI margins have been battlegrounds during cycles featuring candidates akin to Beto O'Rourke in Texas or high-profile Senate fights in Pennsylvania and Georgia. Changes in CPVI preceded notable upsets in special elections such as those analyzed after contests in Virginia and Ohio, and CPVI extremes correlate with long-term polarization trends studied by researchers at University of Notre Dame and Georgetown University.

Category:Political metrics