Fragmented Parties and Strong Presidents Lead to Oversized Coalitions

🧭 Research Puzzle

Presidents in presidential systems routinely use cabinet appointments to build and manage governing coalitions when they lack a legislative majority. Not all coalitions are equal: some are oversized—larger than strictly necessary—and therefore more vulnerable to agency and coordination problems. Existing literature offers several explanations for coalition size, but few tests are systematic and none focus squarely on why surplus (oversized) coalitions form.

🧪 A new dataset covering 168 coalitions across 18 countries (1979–present)

This analysis draws on an original time-series cross-sectional dataset that records 168 unique government coalitions in all 18 Latin American presidential countries since 1979. An additional, more fine-grained test uses monthly cabinet data from Brazil covering 1989–2010.

• Unit of analysis: 168 distinct coalitions in 18 Latin American presidential systems (1979 onward)

• Additional case: Monthly cabinet observations for Brazil, 1989–2010

🧩 Key Findings

The evidence indicates systematic institutional and party-system drivers of oversized coalitions:

• Party-system fragmentation: Highly fragmented party systems make presidents more likely to assemble oversized (surplus) coalitions.

• Presidential powers: Presidents who possess greater formal legislative powers also tend to form larger-than-necessary coalitions.

• Brazilian monthly test: Institutional features such as supermajority rules and bicameralism dynamics increase the incidence of surplus coalitions in Brazil (1989–2010), while measures of party discipline and presidential approval do not.

🏛️ Why It Matters

These results show that oversized coalitions are not merely the outcome of short-term political calculation but are shaped by deeper institutional and party-system structures. The findings have implications for understanding executive-legislative relations, the governance costs of coalition size, and how institutional design (e.g., supermajority thresholds, bicameral arrangements) alters coalition formation incentives.