<HTML><FONT FACE=arial,helvetica><FONT SIZE=2 FAMILY="SANSSERIF" FACE="Arial" LANG="0">Dave you wrote<BR>
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First note: Condorcet considers ALL preferences in pairs simultaneously, <BR>
though often in two steps:<BR>
If one candidate is preferred over each and every other candidate, <BR>
that is the winner. <BR>
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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. <BR>
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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. <BR>
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You also wrote<BR>
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Most of the time IRV and Condorcet produce identical results. We only <BR>
debate around the edges......<BR>
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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.<BR>
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The following assumptions apply:<BR>
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All Conservative voters vote C>LD>LA<BR>
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All Labour voters vote LA>LD>C<BR>
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Liberal Democrat voters vote 50:50 LD>C>LA : LD>LA>C<BR>
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The votes of others have no effect on the election.<BR>
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The votes obtained by the parties were as follows:<BR>
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Conservative (C) 40.5% Labour (LA) 37.2% Liberal Democrat (LD) 17% Others 5.4 %<BR>
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Under FPTP the results were C 9, LA 8, LD 0<BR>
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Under IRV the results were C 7, LA 8, LD 2<BR>
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Under Condorcet the results were C 1, LA 3, LD 13<BR>
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There is a grossly disproportional result under Condorcet The Liberal Democrats obtain 76.5 % of the seats with 17.0 % of the votes. <BR>
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Were the LD vote to increase by 20% an equally bad result would of course be given by IRV.<BR>
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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.<BR>
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Detailed results attached.<BR>
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David Gamble <BR>
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