出典:Wikipedia
出典:『Wikipedia』 (2010/11/14 18:35 UTC 版)
The Gallagher Index (or least squares index) is used to measure the disproportionality of an electoral outcome, that is the difference between the percentage of votes received and the percentage of seats a party gets in the resulting legislature. This is especially useful for comparing proportionality across electoral systems. The index involves taking the square root of half the sum of the squares of the difference between percent of vote and percent of seats for each of the political parties.