ABSTRACT
This chapter addresses the different contexts which can lead to the emergence of political parties with asymmetric viability in the legislative arena, and whether these lead to contamination effects or not. From the supply-side of parties, contamination can be divided between those cases where the phenomenon may come from within the same legislative arena and those other cases where contamination may come from another electoral arena. The chapter deals with the two potential cases of horizontal contamination; namely, from one district to another of the same legislative arena and from the upper to the lower tier in mixed-member systems. It addresses all the hypothetical cases of vertical electoral contamination: from presidential elections; from the upper chamber in bicameral legislatures; and from regional arenas. Finally, from the demand-side of political parties, contamination effects may potentially emerge in the presence of ethnolinguistic heterogeneity. Both institutional and sociological factors have been shown to be able to account for party entrance when non-viable.
