Adopting IRV will cause voter errors ("spoiled" ballots) to become
7 times more frequent
(based on San Francisco numbers).
But adopting range voting appears to decrease errors.
Range voting is monotonic, i.e. increasing your vote for somebody can help
but cannot hurt them.
IRV is not monotonic.
In range voting, scoring your favorite candidate top cannot hurt either
you or him.
In IRV, it can hurt both.
With IRV the "Nader spoiler" and "wasted vote" problems are
contrary to pro-IRV-propaganda.
Indeed, because of fear of these very effects, IRV voters tend to rank third-party
candidates below top (even if favorite) and hence prevent their election,
which presumably is why every
IRV country is and always has been 2-party-dominated.
For this reason IRV cannot attract support from intelligent third-party members.
IRV makes ties and other nightmare-scenarios much more likely;
Range voting makes them much less likely.
IRV is historically more likely than range voting merely to lead to
a backslide to plurality voting.
IRV will (in plausible scenarios)
elect candidate X in preference to candidate Y, even though
based on the IRV votes, Y is pairwise-preferred over X (and over everybody else too)
by an arbitrarily-huge supermajority of
This happened in
the Burlington 2009 mayoral election
and appears to have happened in
both the Peru 2006 presidential election
(but less dramatically; merely a "55% majority" rather than a "huge supermajority" was
thwarted) and the Chile 1970 presidential election
(this time with about a 2:1 ratio supermajority being thwarted).
See also our reports on the
IRV elections and their pathologies.
These were some of the most important IRV
Raising a candidate in your IRV vote from bottom to top-ranked
can actually cause him to lose!