9
Table 3 allows us to measure the party systems previous to the adoption of second-
round presidential electoral systems in ten countries. Again, for each country the effective
number of parties in votes has been calculated for the election immediately previous to the
electoral system change, with an average of 3.9. This also suggests that the replacement of
electoral college or plurality rule presidential elections with absolute-majority or qualified-
plurality rules with a second-round runoff has followed, rather than preceded, the
development of a multi-party system.
During the present democratic periods, presidential elections have been mostly run
with multi-party systems. Table 2 also shows that the average effective number of
presidential candidates in 94 democratic elections in 18 countries has been 3.1. This value
is lower than the corresponding value for congressional elections due to the incentives to
concentrate candidacies and votes in a small number of contenders provided by
majoritarian rules producing a single absolute winner. But the number is still relatively
high, indicating that in most countries multi-partism is not only a feature of congressional
elections but also of presidential ones.
The most important advantage of majority runoff is that the winner at the second
round cannot be the least preferred option of an electoral majority, in contrast to relatively
frequent outcomes with plurality rule. This means that, in the worst of the cases, the elected
president will be considered at least a lesser evil by many of the voters and therefore can
expect to find sufficient popular and political party support to try to build a consensual
political majority around his or her proposals. In more technical terms, while the winner by
majority at a second round may not be the Condorcet winner because he might be defeated
by some other losing candidate in a competition by pairs, he will never be the Condorcet
loser, that is, the candidate that would be defeated in pair-wise contests by every of all the
other candidates, which, in contrast, may be the winner in a contest by plurality rule. This is
so because under majority runoff the Condorcet-loser will be defeated, if not earlier, at least
at the second round.
Qualified-plurality rules establish thresholds at, for instance, 40 or 45 per cent of
popular votes to become the winner, in the proviso that if no candidate attains the threshold
a second-round runoff is held between the two most voted ones. This type of rule, today
adopted (in different forms) in Argentina, Costa Rica, Ecuador and Nicaragua, creates
higher incentives to form broad electoral coalitions already at the first round than plurality
Convention