Matt Golder

In ‘Understanding Interaction Models: Improving Empirical Analyses’, we report the results of several replications that we conducted of analyses examining electoral institutions and party systems. One of these replications was of David Samuels’ article ‘The Gubernatorial Coattails Effect: Federalism and Congressional Elections in Brazil’ which appeared in the Journal of Politics in 2000.

In an article in the Journal of Politics, Samuels (2000) examines the relative impact of presidential and gubernatorial coattails on the composition of the Brazilian party system. Theory would suggest that temporally-proximate presidential and gubernatorial elections should exert a reductive effect on the number of electoral lists in legislative elections. However, this reductive effect should decline (and may become positive) as the number of presidential and gubernatorial candidates increases. Samuels argues that the unusual importance of the governor for office-seeking candidates in Brazilian legislative elections means that we should observe a gubernatorial coattails effect but not a presidential coattails effect in Brazil. This would help to explain why the party system at the national level is highly fragmented (6.3 effective parties), while the party system at the state level is more concentrated (only 3.3 effective parties). The results from three models seem to support his conjecture. However, Samuels draws conclusions from an interaction model that omits constitutive terms. Once these omitted terms are included, none of the coefficients on the variables of interest are significant at the 90% level. Plots of the marginal effect of gubernatorial elections on the number of electoral lists across the observed range of the modifying variable from all three models indicate that gubernatorial elections never exert a coattails effect. While two of the three models indicate that there is no presidential coattails effect either, one suggests that temporally-proximate presidential elections will increase the number of electoral lists if the number of presidential candidates is sufficiently high. Thus, contrary to the conclusions reached by Samuels, the evidence from a fully-specified model indicates that if there is a coattails effect in Brazilian elections then it is a presidential one and not a gubernatorial one. This indicates that gubernatorial coattails cannot explain why the state party system in Brazil is so much less fragmented than the national party system.

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