[EM] Why I think IRV isn't a serious alternative KD

[Juho Laatu]

Here's one explanation to why LNH might be more
important to voters than monotonicity.

Most voters are used to election methods where
they bullet vote one of the candidates. It is a
quite natural thought that if one votes multiple
candidates on a single ballot then the vote that
the second favourite gets may take some power
away from the first favourite. This may not be
based on facts, but of course we don't expect
the voters to be aware of all the technical
properties of the methods.

The voter may be happy and trust the experts if
they tell that this particular method is LNH
compatible and therefore they can mark also their
later preferences without losing power. Also this
may be based on facts but need not be.

Strictly speaking it is enough if it is more
probable that later preferences will help the
voter than that they will cause harm. Therefore a
method that is LNH compatible in 90% of the cases
may be good enough, i.e. the voter could happily
mark also the later preferences in the ballot.

Monotonicity is a similar but reverse case.
Typical voters expect their vote to support the
candidates that they vote for. They don't expect
it to make the results worse from their point of
view. Therefore the voters are not afraid of
non-monotonicity but are happy to vote although
it could be that their vote will make the
results worse.

If the experts would convincingly tell the voters
that their vote may actually lead to a worse
result, then maybe some voters would stop voting
in the hope of improving the results.

But also here it can be claimed that it is enough
if it is more probable that the vote will improve
the results than it is to make them worse.

Voters may thus find LNH more important than
monotonicity. But this does not mean that the
method should be formally LNH compatible. It is
good enough if the methods typically behave as
wanted. It is easier for experts to convince the
voters if they themselves are convinced of their
cause, e.g. as a result of a compatibility proof
that proves that the method meets some criterion
100%.

Sufficient compatibility with the criteria may
thus often be enough. And risks may be higher in
areas where the voters don't expect risks than in
areas where they expect to find them. But the
fact remains that voters may fear some threats
more than others, rationally or irrationally.

Juho


--- On Sun, 21/12/08, James Gilmour <jgilmour at globalnet.co.uk> wrote:

> > The reason I believe LNHarm is more valuable than 
> > monotonicity is that when a method fails LNHarm, the
> voter is 
> > more likely to realize in what insincere way to vote 
> > differently, in order to compensate. When a method
> fails 
> > monotonicity, a voter will rarely know to do anything 
> > differently because of it.
> 
> LNH is important to ordinary electors, as I have explained
> in a recent post, at least where the voting system is
> susceptible to LNH
> effects.  If the vote counting method is not LNH-compliant,
> electors are likely to vote strategically in an attempt to
> avoid or
> mitigate the effects of LNH-failure or to try to gain some
> real or imagined advantage from its effects.
> 
> Monotonicity, or more specifically, the lack of
> monotonicity, is of no importance whatsoever in public
> elections because neither
> candidates nor voters can exploit it.  It would be
> "nice" if the vote counting system were monotonic,
> but we cannot have
> monotonicity AND some of the other criteria we consider
> desirable.  For example, monotonicity and later-no-harm are
> incompatible in
> IRV and STV-PR.  Of the two, LNH is important  - 
> non-monotonicity is irrelevant.
> 
> James Gilmour
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