[EM] Margins vs. Winning Votes

[Dave Ketchum]

On Wed, 20 Jul 2005 21:36:00 +0300 Juho Laatu wrote:

> Hi All,
> 
> Here is one interesting margins vs. winning votes example for you to 
> consider. I don't remember having seen this type of scenario. But with 
> good probability someone has already analysed this, so please provide 
> some pointers if this has been discussed on the list or elsewhere.
> 
> The example is a bit more complex than it would need to be. That is 
> because I prefer presenting it as a real life example instead of a 
> theoretical extreme case. This example fits nicely within the framework 
> of the the US presidential elections. Few observations follow.
> 
> 20    A
> 15    ABC
> 10    ACB
> 35    BC
> 20    CB
> 
> - Democrats have nominated candidate A.
> - Republicans have nominated two candidates. In addition to their normal 
> mainstream candidate B they have nominated also a right wing candidate C.
> - All voters have taken position on Democrats vs. Republicans.
> - Some Democrat voters have not taken position on the Republican 
> internal battle between B and C.
> - All Republican voters have taken position on B vs. C.
> - Democrats prefer B over C.
> - Republicans prefer B over C.
> - B is the Condorcet winner.
> - In raking based real life elections it seems to be quite common that 
> voters don't give full rankings. This example has only three candidates 
> and therefore full rankings could be quite common. But the election 
> could have also considerably more than three candidates, in which case 
> partial rankings probably would be quite common. It is probable that 
> ranking candidates of competing party is less common than ranking 
> candidates of ones own party (just like in this example).


Partial rankings ARE appropriate - you properly do not rank when you do 
not know or care which of the leftovers are better.

> 
> Now, what if some of  the the 20 C supporters (C>B voters) would note 
> the weak position of C before the election and decide to vote 
> strategically C>A>B.


The word "strategically" turns me off.  For whatever reason, they are 
switching between C>B>A (with A's position implied) and C>A>B - between B 
is preferable to A to A is preferable to B.
      Not surprising that B no longer wins.
      Not surprising that C wins in WV - C retains its ranking while B 
becomes less desirable.
      Perhaps less surprising that A wins in margins - these voters were 
SUCCESSFUL in controlling outcome between A and B (though they were unable 
to cause C to win).


> - in the case of winning votes C wins the election with 6 to 20 
> strategic votes (out of the 20 C>B votes)
>     => quite efficient and risk free (if one has reliable opinion poll 
> results available) (and if others don't use other strategies)
> - in the case of margins A wins the election with 11 to 20 strategic 
> votes (out of the 20 C>B votes)
>     => not very promising as a strategy
> 
> Yours,
> Juho

-- 
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  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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