Condorcet Truncation Example

[Markus Schulze]

Dear Rob, dear Hugh,

you did me wrong. I have never said, that Smith//Condorcet [EM]
is not "truncation resistant" due to your definition of "truncation
resistant".

The problem looks a little bit different: Usually only downward
truncation [i.e., the voter gives his worst preference to more
than one candidate] is discussed, because usually only plain
Condorcet is discussed. And if plain Condorcet is discussed, 
downward truncation is a usefull strategy.

But the way you have defined "truncation resistant" and
Smith//Condorcet [EM], the following problems will occur:

(1)Upward truncation [i.e., the voter gives his best preference
   to more than one candidate] becomes a usefull strategy,
   especially if there is the danger that more than one of the
   most favoured candidates comes into the Smith set and one of
   the most favoured candidates in the Smith set would have his
   highest defeat against another of the most favoured candidates
   in the Smith set.

(2)Distributing the worst preferences random among the least
   favoured candidates becomes a usefull strategy. That means:
   If the voter doesn't care, who of his least favoured 
   candidates wins [if one of them should win], then it is
   nevertheless the best strategy to give them different
   preferences to maximize the chances of a favoured 
   candidate to win.

Again: Even if none of the other voters votes tactically,
every Condorcet Criterion method punishes those voters, who
give full information about their true opinion. This means, that 
they won't give full information about their true opinion.
This means, that it won't be possible to determine the 
Condorcet Criterion winner due to the opinion of the voters
even if no voter votes tactically. This means that the Condorcet
Criterion method won't work.

This is what is meant, when it is said in literature, that 
"truncation" is a problem of any Condorcet Criterion method.

Markus Schulze (schulze at speedy.physik.tu-berlin.de)