PlanScore presents estimates of how severe state's gerrymander is by measuring today's maps against historical data.
At the congressional level, we relied on election results from the Constituency-Level Elections Archive, Cook Political Report, and Dave Leip’s Atlas of U.S. Elections. Data on presidential vote and incumbency status came from a variety of sources, including Gary Jacobson, Gary King, The Downballot, and aggregation of precinct-level data from the Voting and Elections Science Team.
At the state legislative level, Carl Klarner of Klarner Politics provided us with all of the relevant election data and incumbency status. Data on presidential vote came from a variety of sources, including The Downballot, Steve Rogers, and aggregation of precinct-level data from the Voting and Elections Science Team.
Methodology for current version of PlanScore historical data:
The Impact of Partisan Gerrymandering on Political Parties, Nicholas Stephanopoulos and Christopher Warshaw’s February 2020 article for Legislative Studies Quarterly.
Assessing the Current Wisconsin State Legislative Districting Plan, Simon Jackman’s 2015 expert witness report in Gill v. Whitford, analyzing state legislative plans.
Assessing the Current North Carolina Congressional Districting Plan, Simon Jackman’s 2017 expert witness report in LWVNC v. Rucho, analyzing congressional plans.
Chris Warshaw, Simon Jackman, Eric McGhee, and Nicholas Stephanopoulos compiled these estimates in their academic and litigation-related work.