These are the two principal components of 13-15 indicators of democracy, including those compiled by Freedom House; Polity; Arthur Banks; Alvarez, Cheibub, Limongi, and Przeworski, as updated by Cheibub and Gandhi; Bollen; and Cingranelli and Richards. The dataset covers most countries in the world from 1950 through 2000. In an article in the Journal of Politics (July 2008), the authors argue that these principal components, which capture 75 percent of variation in the most commonly used democracy indicators, measure Robert Dahl's two dimensions of polyarchy: contestation and inclusiveness.