Party Systems and Government Stability

Arguments are presented for and against a series of hypotheses about the influence of the parliamentary party system on the stability of governments, and the hypotheses are tested against data on 196 governments in parliamentary democracies since 1945. A strong relation is found between the duration of governments and the fragmentation of the parliamentary party system and of the government parties, but the fragmentation of the opposition parties seems not to affect stability. One-party governments are more stable than coalition governments, and majority governments more than minority governments. The ideological dispersion of the parties—in the whole parliament, in the government, or in the opposition—does not explain stability any better than fragmentation, which is based upon only the number and sizes of parties; but the proportion of seats held by ‘anti-system’ parties (communists and neo-fascists, mainly) is a good indicator of stability. The best explanation of government stability found here is the combined linear influence of the size of the anti-system parties and the fragmentation of the pro-system parties.