[EM] voting strategy with rank-order-with-equality ballots

[Juho Laatu]

I have a rather practical approach to
strategies. Often we talk about theoretical
properties of the methods. I prefer talking
about the practical impacts (of the known
theoretical vulnerabilities) since often
the theoretical cases talk only about some
marginal cases. I'll explain more below.

Schulze and Condorcet methods in general
may sometimes be vulnerable to strategies
where voters change some ">" to "=". You
however did not present and I do not know
situations where it would be beneficial
(strategically) to generally vote in
approval style in Schulze/Condorcet.

My practical approach is such that when
some theoretical vulnerability has been
identified I try to construct also a
practical example (in some well defined
real life environment) to see if it
really is a threat. One needs to
understand also the dynamics of the
problem in real life situations.

Topics to consider:
- how often does the vulnerability occur
- what information do the voters have
- is that information reliable
  - unreliable polls
  - opinions may change
- can voters apply the strategy on their own
  - media or party guidance may be needed
  - maybe a general rule for all elections
- does the strategy require coordination
  - agreed voting pattern
  - different strategists to vote in different ways
- will others know about the planned strategy
- are there counter-strategies?
- how "bad" is the change in the outcome
- can the strategy backfire

There are also many society related aspects:
- what are the impacts of strategy proposals
  - all become strategic?
  - strategists will lose support?
- what is the tradition of the society
  - strategic vs. sincere
  - is strategic voting morally acceptable
- are the voter opinions stable or changing
  - party loyalty
- are the polls used as propaganda
- is the election large or small
- do the voters make independent decisions
  - or do they follow party guidance
- number of candidates and parties and groupings
- great variety of opinions vs. just few patterns
- impact on the next elections and society
  - e.g. strategic votes to unwanted candidates

Practically all methods have vulnerabilities,
so we just need to pick methods that are good
enough in the given environment. One should
also note that often there is also the other
side of the coin. When defending against one
threat one may open doors to other threats or
otherwise make the system worse. (Note that
this also means that sometimes it is better to
have numerous weak vulnerabilities rather than
only one more serious vulnerability, i.e. just
listing the individual vulnerabilities does
not work.)

(One should btw also make sure that the
behaviour of the used method can be justified
also with sincere votes. Electing a "wrong"
candidate with sincere votes is about as bad
as electing a wrong candidate due to strategic
voting.)

Based on this kind of checklists I think
it is often quite easy to quickly come into
conclusion on if the discussed vulnerability
is a serious threat or just theoretical.

The theoretical vulnerabilities are important
as a basis of the studies but often practical
examples of typical but bad situations that
may occur in the given environment demonstrate
better what the actual performance level of
some proposed system is.

Practical group strategies that can be applied
by individuals without central coordination
are the most interesting ones. Counter
strategies are already much less interesting
(things are already quite bad if people really
start using them).

Now back to the discussed methods. It is
characteristic to Schulze and Condorcet
methods that their vulnerabilities are
severe in the sense that in some cases some
group may indeed (at least in theory) change
the outcome of the election, but those
strategies are not very easy to identify,
not very common and may easily backfire. As
a general rule voters' best strategy is
often to vote sincerely. In Range one big
problem is that exaggeration seems to work
quite generally. For example in a typical US
presidential election a general
recommendation of all Democrats to vote D=max
R=min is not a bad strategy to follow. In
Condorcet finding a working strategy (other
than sincerity) that could be generally
recommended to the voters would not be that
easy.

Juho


--- On Tue, 9/6/09, Warren Smith <warren.wds at gmail.com> wrote:

> One problem is nobody really has a
> good understanding of what good strategy is.
> 
> If one believes that range voting becomes approval voting
> in the
> presence of strategic voters (often, anyhow)...
> 
> One might similarly speculate that
> strategic voters in a system such as Schilze beatpaths
> ALLOWING ballots
> with both > and = (e.g. A>B=C=D>E=F is a legal
> ballot)  usually the
> strategic vote
> is "approval style" i.e. of form A=B=C>D=E=F, say, with
> just ONE ">".
> One might then speculate that Schulze, just like range,
> then becomes
> equivalent to approval voting for strategic voters.
> 
> Well...  how true or false is
> that?   Is Schulze with approval-style
> ballots
> a better or worse voting system than plain approval?
> 
> How true is it that approval-style voting is "strategic"
> for Schulze?
> 
> I'd like to hear people's ideas on this question. 
> (And not
> necessarily just for "Schulze" -- substitute other methods
> too, if you
> prefer.)
> 
> The trouble is, range voting is simple. Simple enough that
> you can
> reach a pretty full understanding of what strategic range
> voting is.
>   (Which is not at all trivial,
> but it can pretty much be done.) In contrast, a lot of
> Condorcet
> systems including Schulze are complicated. Complicated
> enough that
> making confident statements
> about their behavior with strtagic voters (or even
> undertsnading what
> strtagy IS) is
> hard.
> 
> Frankly, I've heard various vague but confident claims
> about strategy
> for Schulze & the like, and my impression is those
> making the claims
> know very little about what they
> are talking about.  I also know very little on this,
> the difference is
> I admit it :)
> 
> 
> -- 
> Warren D. Smith
> http://RangeVoting.org  <-- add your
> endorsement (by clicking
> "endorse" as 1st step)
> and
> math.temple.edu/~wds/homepage/works.html
> ----
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