Who gains from apparentments under D'Hondt?

Apparentments - or coalitions of several electoral lists - are a widely neglected aspect of the study of proportional electoral systems. This paper proposes a formal model that explains the benefits political parties derive from apparentments, based on their alliance strategies and relative size. In doing so, it reveals that apparentments are most beneficial for highly fractionalised political blocs. However, it also emerges that large parties stand to gain much more from apparentments than small parties do. Because of this, small parties are likely to join in apparentments with other small parties, excluding large parties where possible. These arguments are tested empirically, using a new dataset from the Swiss national parliamentary elections covering a period from 1995 to 2007.