Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I say who wrote them.
Desposato. 2004. The impact of electoral rules on legislative parties: Lessons from the Brazilian Senate and Chamber. Unpublished.
Do electoral institutions affect (legislative) party organization?
Many argue that electoral institutions determine whether politicians have personal (pork) or party (public goods) incentives. In the Brazilian case, they cite open-list PR as the cause of Brazil's weak party system. But the fact that electoral institutions create incentives for personalistic politics in the electorate does not imply that party discipline will be weak in the congress. For a supporting argument, see Figueiredo and Limongi (2000).
Though many study the Brazilian Chamber (lower house), few study the Senate, which has similar powers but very different electoral rules. Senators are elected in plurality districts (more or less). Thus, if the literature is correct, we should observe less developed parties in the Chamber than in the Senate. Desposato looks specifically at a few indicators (Y) of this:
Each state gets three Senators, serving staggered eight-year terms. Thus, one Senator seat was open in each state in 1990 and 1998, and two seats were open in each state in 1994 and 2002. So 1990 and 1998 were plurality elections, and 1994 and 2002 were two-member district plurality elections (each voter could vote for two candidates).
Research on similar subjects