States are ranked in each of the following categories:

Democracy Index: Measure of a state’s average ranking in key categories: average margin of victory (measuring overall competitiveness), landslide index (measuring the number of somewhat competitive races), seats-to-votes distortion (measuring how well the intent of voters was reflected by the results), and representation index (weighted double, as it measures both voter participation and the percentage of effective votes that elect someone).

Average Margin of Victory: Measure of the average in a state's House races of the winner’s percentage of the vote minus the second-place candidate’s percentage of the vote.

Seats-to-Votes Distortion: Measure of the average by which one party wins a greater percentage of seats than votes and the other party wins a smaller percentage of seats than votes. The distortion is calculated by adding the percentage distortion for each party and then dividing by two. For example, if Democratic candidates won 10% more House seats than votes and Republicans won 6% fewer House seats than their share of the House votes, the seat-to-vote distortion would be 8%.

Landslide Index: Measure of the percentage of all U.S. races won by a margin of victory of at least 20 percent.

Representation Index: Measure of the percentage of eligible voters in a state who voted for the winning candidate in US House elections. The index is determined by multiplying the voter turnout in US House races by the percentage of votes cast for winning candidates.

Voter Turnout: Measure of the percentage of the voting eligible population who voted in a state’s US House elections (as opposed to statewide and presidential elections). We use population estimates by Professor Michael McDonald at George Mason University. His figures estimate the number of voting age adults who are eligible to vote, which means they exclude non-citizens and other adults who cannot vote, and estimate eligible overseas voters from that state.