Spoiler effects in proportional representation systems: evidence from eight Polish parliamentary elections, 1991–2015

I consider a model of multiple winner elections with several types of spoilers. In single-office elections, a “classic” spoiler turns a winner into a non-winner and a non-winner into a winner. Such spoilers rarely appear in multi-office elections. In such elections, spoilers include a “Kingmaker”, who turns a non-winner into a winner; a “Kingslayer”, who turns a winner into a non-winner; a “Valuegobbler”, who subtracts from some competitor more seats than it receives; and “Selfspoilers”, who may be hurt by competing separately rather than creating an electoral coalition. Various strategic spoilers, such as fake parties, are possible as well. I look for spoilers in eight Polish parliamentary elections that have taken place since the fall of communism in 1989. In two elections, the consequences of spoilers were massive. In 1993, multiple spoilers on the right helped the two post-communist parties return to power, slow down decommunization and create strong institutional obstacles to further democratization. In 2015, a spoiler manufactured a majority for the largest party (PiS) and, as a consequence, enabled PiS quickly to implement radical reforms. In other elections, spoilers had smaller, but noticeable consequences. The results suggest that parliamentary elections using PR party-list systems are vulnerable to spoiler problems that may cause significant political effects.