single-winner district and where the probability distribution of votes is known (perfect information). Converse Two-party politics may emerge in systems that do not use the plurality vote, especially in countries using systems that do not fully incorporate proportional representation. For instance, Malta has a single transferable vote (STV) system and apparently stable two-party politics. Some systems are even more likely to lead to a two-party outcome: for example, elections in Gibraltar use a partial block vote system (which is classified as majoritarian) in a single constituency, so the third most popular party is unlikely to win any seats. In recent years some researchers have modified Duverger's law by suggesting that causal influence between electoral and party systems might be bidirectional or in either direction. It has been shown that changes from a plurality system to a proportional system are typically preceded by the emergence of more than two effective parties, and increases in the effective number of parties happens not in the short-term, but in the mid-to-long term. See also References External links Dunleavy, Patrick, Duverger’s Law is a dead parrot. Outside the USA, first-past-the-post voting has no tendency at all to produce two party politics Voting theory