Effective Number of Parties
Measuring how many parties, weighted according to size, are in a party system in a given election, the effective number of (electoral/parliamentary) parties is calculated employing the following formulae:
where vi/si is the proportion of votes/seats of the ith party (see Laakso and Taagepera, 1979; Casal Bértoa, 2013: 401-402).
Please cite the following database as: Casal Bértoa, F. (2016): Database on WHO GOVERNS in Europe and beyond, PSGo. Available at: whogoverns.eu