[Election-Methods] Why monotonicity? (was: Smith +mono-add-top?)

James Gilmour jgilmour at globalnet.co.uk
Thu Jan 10 02:05:58 PST 2008

daniel radetsky > Sent: 10 January 2008 03:09
  (comments taken in reverse order)
> In any case, resistance to manipulability is not the only 
> reason to desire a particular property for a voting system. 
> Another important quality is transparency: does casting a 
> vote do what the voter thinks it does? A voter thinks that 
> when he increases his vote for X (whatever "increases" means 
> in the system in question), he is helping X win. In a 
> non-monotonic system, he's wrong, or at least not guaranteed 
> to be right. This is bad. Right? 

Right.  But to put correct this defect we have no option but to sacrifice something else, e.g. "later no harm".  And some of us
think "later no harm" is MUCH more important than monotonicity, especially as non-monotonicity cannot be manipulated either by the
candidates or by the voters in any election with significant numbers of voters.

> However, I was under the impression that one of the goals of 
> studying voting methods was to avoid having to make this choice. 

That would be nice, but all the evidence to date shows that it is impossible.  No-one has yet devised a voting system that
incorporates all of the desirable features.  Some of them appear to be mutually incompatible.

James Gilmour

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