Duverger’s Law

Recent elections that have produced coalition governments in Australia and the UK have prompted claims that Durverger’s Law, a plurality rule electoral system tends to favor a two-parties, is failing. I think claims of Duverger’s death have been exaggerated.

First, as Gary Cox observed in Making Votes Count, Duverger’s Law holds at the district level, not the national level. That a plurality system could produce two parties at the district level, but many more at the national level is perfectly consistent with Durverger’s Law.

Second, its not clear that Australia’s election was that much of an outlier. Examining the district-level returns (where we expect Duverger’s Law to hold) shows that on average there were 2.6 effective parties in its 2009 election in each single-member electoral district. This is only a bit higher than Australia’s long-term average of 2.3 and not that much higher than the US’s long-term average of 2.4.

I think its a pit premature to put a toe tag on Durverger’s Law.