What political effect does the switch from Plurality to Instant Runoff voting have?

This article:

Lauri Karvonen: Preferential Voting: Incidence and Effects, International Political Science Review 25,2 (April 2004) 203-226

found that, contrary to IRV propaganda, the switch from plurality to IRV voting empirically has little political effect. In particular, it does not get rid of 2-party domination.

Abstract: Many democratic voting systems simply present voters with a choice between parties, while others give them the opportunity to choose among individual candidates as well. This article focuses on the latter type of electoral systems, that is, those allowing for preferential voting. A classification according to the degree and type of candidate choice is presented, and the electoral systems of some 70 democracies are classified with the aid of this scheme. Preferential voting proper is found to be largely a western European phenomenon. Eight hypotheses concerning the effects of preferential voting on party systems, parties, candidates, and voters are tested. Overall, the impression is that preferential voting has few discernible effects at the aggregate level.

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