Wikipedia:Reference desk/Archives/Mathematics/2011 September 22

= September 22 =

Mixed Member Proportional Voting and Gerrymandering
Because of overhang seats in some MMP systems, it it still possible to gerrymander the constituencies to take advantage of this effect to get a larger portion of seats for your party? Obviously the effect would not be as great as with FPTP, but is it still technically possible? --CGPGrey (talk) 07:45, 22 September 2011 (UTC)
 * I guess, but the effect (disproportionateness) is larger the less popular (in terms of party vote) a party is, and less popular parties don't have all that much opportunity to gerrymander, so in practical terms it doesn't mean much. However, if there is no threshold, then under the Sainte-Laguë method of apportioning seats, very small parties are able to gerrymander themselves by splitting into smaller parties. For example, in New Zealand at the last election, if there had been no threshold, a party would have been able to get in (with one MP) with something like 0.43% of the vote. If a party got 1% of the vote, they would also have gotten 1 MP (I think - I'll have to doublecheck that later on). If such a party split and ran as two independent parties, each attracting half of the original party's votes, then each would get 1 MP. --130.216.55.172 (talk) 04:08, 23 September 2011 (UTC)