title:         Party Incumbency as a Source of Contamination in Mixed Electoral Systems
authors:       Jens Hainmueller, Holger Lutz Kern
entrydate:     2006-03-10 09:08:44
keywords:      contamination,mixed electoral systems,causal inference,regression-discontinuity design
abstract:      We identify party incumbency as a new source of contamination in mixed electoral systems. We argue that party incumbency not only boosts SMD vote shares; it also has a positive effect on vote shares in the PR tier of mixed electoral systems. This effect has been overlooked in the contamination literature so far. We test our hypothesis with data from German federal elections
and employ a regression-discontinuity (RD) design in order to overcome some
of the obstacles to reliable causal inference in observational studies. The RD
design exploits the random variation in party incumbency status that occurs when a district race is close and thus allows for causal inference under a weaker set of assumptions than the regression models commonly used in the electoral systems literature. We find that party incumbency results in a gain of about 1 to 1.5 percentage points in PR vote share, which according to simulation results is potentially sufficient to trigger significant shifts in Bundestag majorities.

http://polmeth.wustl.edu/retrieve.php?id=586

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