Abstract:

In proportional representation systems voters vote for parties or blocks, which run for the certain number of seats in a representative body, and get seats proportionally to the received votes. In what degree the elected parliament reflects the interests of various groups of the voters, or, in other words, to which extent it is representative? To answer this question the indices are introduced evaluating the degree of proportionality of an electoral system, called "disproportionality indices". Disproportionality indices are based on the comparison between the number of votes and number of seats each party obtains. In the article the reasons why any electoral PR system distorts voters’ preferences are discussed. Below we describe several well-known proportional representation systems, give a brief look to known disproportionality indices and introduce two new indices of that type, the Representation Index and the Index of Relative Representation, respectively. These two indices are calculated for parliamentary elections in several countries.

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