Is an index of seats held by the largest party, obtained by Size of Legislature divided by Number of Seats, Largest Party in Legislature. The principal reason for calculating the index in this manner (rather than as a percentage of seats held) is to ensure that the indices for countries with no parties (or no legislatures) and countries with one-party systems will be adjacent, rather than at opposite extremes of the array. Thus a country with no parties has a score of 0, a one-party system has a score of 1.0, a system with 40 out of 100 seats held by the majority party has a score of 2.5, etc.