Australia is one of the few places to use preferential voting, but many
countries use a system designed to achieve the same effect – the
run-off election. When no candidate receives an absolute majority of
the votes, a second poll is held between the top two candidates, thus
ensuring that the winner has majority support.

The advantages of this over preferential voting are clear: voters don’t
have the difficulty of having to number their ballots, and when a
second round is needed they can concentrate on the single choice that
matters, instead of a large number of preferences that will mostly have
no effect on the result.

But it has its problems, as last week’s election in Haiti
demonstrates. With 75% of the vote counted, front-runner Rene Preval is
just short of a majority, on 49.1%. His tally has been dropping as
votes from more conservative rural areas come in, so it seems likely
that a run-off will be required.

There is no doubt, however, that Preval has won. The other 51% of the
vote is spread among 34 other candidates; Preval’s nearest rival,
Leslie Manigat, is back on 11.7%. (Adam Carr’s Psephos has a list
from an earlier stage of counting.) If Haiti had preferential voting,
the elimination of a few also-ran candidates would be enough to ensure
Preval’s election. This is why in the United States preferential voting
is generally referred to as an “instant run-off” system.

In a country like Haiti the issue is much more important than just the
cost of an unnecessary run-off. Neither side trusts the fairness of the
process, and an unnecessary poll increases suspicions and raises the
likelihood of violence. Preval’s supporters have been demonstrating in
the streets for the last two days demanding that he be declared the
winner.

Some countries try to avoid the problem by setting a threshold of less
than 50% for the run-off. In Costa Rica, which also voted last week, it
was 40% – which would have worked well in Haiti. But it worked very
badly in Costa Rica, because two candidates each got fractionally over
40%, with only 0.2% between them. So no run-off will be held, but
whoever is the winner (a recount is under way) will lack a clear
mandate, since it is clear that either a run-off or a preferential vote
could have changed the result.