[EM] Margins vs. Winning Votes

[Juho Laatu]

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).

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.
- 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