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How to Operationalize Two-Partyness


Because of the prominence of Duverger's law, a great deal of work has focused on assessing whether or not given election outcomes can be regarded as exhibiting two-party competition. The most common metric for assessment is whether the effective number of parties is close to two. We introduce two statistics that better measure conformity to two-partyness, briefly survey their logical properties, and then demonstrate their utility with data on parliamentary elections in England. © 2013 Elections, Public Opinion & Parties.

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