Costa Rica’s record fragmentation

I already said this in a comment at an earlier thread, but it is the sort of thing that is at the very core of Fruits & Votes, and hence deserves its own space…

By my calculation, the effective number of vote-winning parties in Costa Rica’s 2 Feb. election was 6.21. The effective number of presidential candidates was 4.36. Both easily break the record for the country’s elections back to 1953. The old averages and maximums were 3.21 and 4.84 for vote-winning legislative parties and 2.37 and 3.30 for presidential candidates. (Historical figures based on Bormann and Golder’s dataset.)

Costa Rica’s party system sure is unrecognizable from what it was for so long!

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The effective number of parties or candidates is by now the most well established measure of electoral or legislative fragmentation. It is simply a weighted count of the number of components (parties, candidates, or anything else) where the components are weighted by their own size through squaring them. Operationally: square each component’s share (out of 1), sum the squares, and take the reciprocal of the sum. Originally proposed by Laakso and Taagepera in a 1979 article.

2 thoughts on “Costa Rica’s record fragmentation

  1. Is it hard for the parties in Costa Rica’s Congress to pass bills? Despite the fragmentation, Costa Rica has a very small legislature at 57 members, if it were larger, were more parties be represented in it?

    What is the history of proportional representation in Latin America? What was the reason for it? Does it work well with Presidentialism? Are there lessons for the U.S?

  2. Completing the picture, the effective number of parties by legislative seats in the 2014 election was 4.92. The mean value for 1953-2010 was 2.66, and the previous maximum was 3.90 in 2010.

    (Calculated for 2014 from seats data posted by Manuel at Election Resources on the Internet; previous values from Borman and Golder.)

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