More on Measuring Two-Party Competition: A Response to Dunleavy

Gaines and Taagepera [(2013) How to operationalize two-partyness. Journal of Elections Public Opinion and Parties, 23(4), pp. 387–404] propose two indices of two-party competition for district-level data, both of which are alleged to be flawed. The case against them rests mainly on whether or not elections with one dominant party should be regarded as exhibiting one- or two-way competition. For those inclined to see 90–10% and 50–50% outcomes are different in kind, our indices can provide better measures than the popular effective number of parties or the “gap”. We agree that assessment of a set of outcomes, in a given election or over time, requires careful attention to the important distinction between micro-level data and aggregate measures.