This data set contains the raw election data and an analysis of partisan advantage in all U.S. House races as well as about 4,900 state House and Assembly races in both 2018 and 2016 elections.
The analysis, conducted by the Associated Press after the 2016 and 2018 elections, used a mathematical formula called the "efficiency gap" to measure partisan advantage in the elections. The statistical analysis is designed to detect cases in which one party may have won, widened or retained its grip on power through partisan gerrymandering, the process of drawing congressional and state legislative seats to favor the majority party.
To produce efficiency gap scores for each state, the AP obtained vote totals for all U.S. and state House elections and calculated the share of the votes received by Republicans and Democrats in each district, excluding votes cast for independent and third-party candidates. From those figures, the AP calculated the statewide average share of the vote that each party received in state legislative races, and then compared that figure to the party's share of the seats won in that state.
This data set includes four files:
- State-level vote totals and efficiency gap calculations for the 2018 U.S. House elections. Seven states have only one U.S. House seat and aren't included. North Carolina's calculations are based on its 12 certified districts.
- State-level vote totals and efficiency gap analysis for U.S. House races for the 2016 elections. Seven states have only one U.S. House seat and thus have no district data. Those states are Alaska, Delaware, Montana, North Dakota, South Dakota, Vermont and Wyoming.
- Efficiency gap analysis on state legislature races for House or Assembly seats in 2018. Six states excluded from the data (see caveats): Louisiana, Mississippi, Nebraska, New Jersey, North Dakota and Virginia.
- Efficiency gap analysis on state legislature races for House or Assembly seats in 2016. Eight states are excluded from the data (see caveats): Alabama, Louisiana, Maryland, Mississippi, Nebraska, New Jersey, North Dakota and Virginia.
Additional details about the methodology and findings from the Associated Press analysis are available in the documentation included with purchase, as well as in the sample download available on this page.
Provided in collaboration with Associated PressProPublica & Associated Press