[EM] Is Condorcet The Turkey?

[Dgamble997 at aol.com]

Dave you wrote

First note: Condorcet considers ALL preferences in pairs simultaneously, 
though often in two steps:
If one candidate is preferred over each and every other candidate, 
that is the winner. 
    
This is exactly what I meant. Condorcet simultaneously compares all pairs of 
candidates. The voter, has for example, ranked the candidates A 1st, B 2nd, C 
3rd, D 4th, etc. In simultaneous paired comparisons the 4th Preference D is 
rated as having equal value to the 1st preference A. In pairwise comparisons 
between A and another candidate E this A>B>C>D vote counts one for A, likewise in 
a similar DE pairwise comparison it will count one for D. Since the voter has 
ranked A 1st and D 4th s/he clearly supports A more than D. 

IRV has the advantage that lower preferences are not considered until higher 
preferences have been eliminated. This removes the problem that A is preferred 
to D and yet in a Condorcet count both are counted as one against candidate 
E. If A, B and C are eliminated we can assume (safely) the voter will 
wholehearted support D as his/her highest choice remaining in the count. 

You also wrote

Most of the time IRV and Condorcet produce identical results. We only 
debate around the edges......

You statement is probably true regarding the American party system - both IRV 
and Condorcet will probably give a congress composed entirely or almost 
entirely of Democrats and Republicans. However for the British party system (the 
one I'm most familiar with) this is not the case. Since the 1930's the UK has 
had three parties. A large party on the right ( Conservative), a large party on 
the left (Labour) and a smaller party ( variously the Liberals, Alliance, 
Liberal Democrats ) between the two. I attempted an analysis of the results of the 
1997 General Election for the 17 seats in the county of Kent under FPTP, IRV 
and Condorcet.

The following assumptions apply:

All Conservative voters vote C>LD>LA

All Labour voters vote LA>LD>C

Liberal Democrat voters vote 50:50 LD>C>LA : LD>LA>C

The votes of others have no effect on the election.

The votes obtained by the parties were as follows:

Conservative (C) 40.5% Labour (LA) 37.2% Liberal Democrat (LD) 17% Others 5.4 
%

Under FPTP the results were C 9, LA 8, LD 0

Under IRV  the results were C 7, LA 8, LD 2

Under Condorcet the results were C 1, LA 3, LD 13

There is a grossly disproportional result under Condorcet The Liberal 
Democrats obtain 76.5 % of the seats with 17.0 % of the votes. 

Were the LD vote to increase by 20% an equally bad result would of course be 
given by IRV.

The moral of this story of course is that there is little proportional  about 
the allocation of a single seat and even less proportional about the sum of 
the allocation of a series of single seats.

Detailed results attached.

David Gamble    


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