Voting after the change: A natural experiment on the effect of electoral reform on party system fragmentation

This article analyses the causal effect of the 1993 electoral reform in New Zealand on party system fragmentation using the ‘synthetic’ control method. Previous studies using cross-national evidence suggest that electoral reforms change the number of parties. However, they do not take into account possible endogeneity problems and usually focus on their short-term effects. Since the electoral system in use in this country before the change was first past the post (FPTP), I can create a ‘synthetic’ control democracy that had the same institutional framework but did not modify the rules of the game. The results indicate that the electoral reform produced the expected effects on party system size at the electoral level, but that these effects tended to disappear in the long run. In contrast, electoral system effects at the legislative level were larger and stickier over time.