(Executive Summary) (skip to conclusions) With plurality voting,
your ballot can be invalidated by voting for two candidates
(overvoting). With instant runoff voting, there are more ways to
go wrong. E.g. you can co-rank two candidates at any level of
the ranking, skip a ranking-level, etc. So it seems "obvious"
there are going to be higher ballot spoilage rates with IRV than
with plurality. With range and approval voting, there are fewer
ways, in fact many would say no ways, to go wrong, because every
way to vote or to fill out numbers within the permitted range,
is a valid vote. So you similarly might expect range and
approval voting to have lower spoilage rates than plurality. All
that, however, is just a theory. The real proof of the pudding
is the experiment. As PhD advisors are fond of saying to their
poor graduate students, "Show me the data!". According to
official plurality-vote totals: Florida's ballot spoilage rate
in 2000 was 3%, and for the US nationwide 2000 presidential
election, 1.9 million ba