How the AP did its analysis of partisan advantage in US House districts

The Associated Press used to examine congressional elections in 2024 and other recent presidential election years.

The test — designed by Eric McGhee, a researcher at the nonpartisan Public Policy Institute of California, and Harvard Law School professor Nick Stephanopoulos — identifies states where one party is extraordinarily efficient at translating votes into victories in legislative districts. The larger the efficiency gap, the greater the advantage that either Democrats or Republicans received from the way district boundaries were drawn.