Comments on: Condorcet rules?

By: shooting_star

shooting_star — Wed, 03 Mar 2004 00:11:12 +0000

I was hoping Condorcet would come up when I posted my comments on the previous STV page about voting systems. John Quiggen seems to prefer Proportional Representation to centrism. Well, the whole point of a Condorcet ballot is that a candidate has to appeal to multiple groups to elevate his preferences. Borda can be rigged toward extremism by pushing the main opposition candidate toward the bottom. But there is no advantage to doing this in a Condorcet system. Condorcet may seem complex, but it is exactly what pollsters do—they match up all candidates with each other in head-to-head contests. I don’t think this is too hard for voters to understand. Approval is a reasonable alternative to Condorcet and also tends to choose the more centrist candidate. And it also can be polled for easily, so voters will have a better sense of the likely outcome if they want to change their votes. Proportional Representation has its place, but it isn’t in a single winner election. You really want PR in an assembly. The known problems with Condorcet occur when you get cyclic rankings. So you need a rule to decide which victories you want to include and which you don’t. Ranked Pairs / Maximize Affirmed Majorities is a reasonably understandable way to handle this. It isn’t hard to do. Pick the largest victory (by total number of votes), include the next largest victory, and leave out any victories that cause a cycle. You’re left with an unambiguous ranking. Brian Weatherson’s example is interesting. The Condorcet victor would be C (beats B 53:47, beats A 52:48, B beats A 52:48). C is the second choice of a nearly divided set of 95 voters who really dislike the majority opposition candidate (A or B). In STV, you get 47 happy B voters and 5 semi-satisfied C voters, but 48 very dissatisfied A voters. If you set the last choice candidate to non-approved, the Approval winner would also be C, with 95 votes C to 52 B to 48 A. So why should a candidate with lower approval win via STV? It’s only natural if you think using the logic of caucuses, where small losing blocks can sway the plurality when they switch allegiance.

By: Brian Weatherson

Brian Weatherson — Tue, 02 Mar 2004 22:24:02 +0000

I’d be more impressed with the criticism that STV rewards tactical voting if there were more actual examples adduced of tactical voting being rewarded. There have been tens of thousands of elections run under STV in Australia (just counting Federal, State and local elections) and there are no clear cases of this kind of tactical voting making a difference, and only a handful of cases where it is even plausible to claim tactical voting might have mattered. Maybe it’s just indoctrination into the STV system, but when I see a case like the following, I think it’s natural that B should win. 48 votes for A then C then B 47 votes for B then C then A 5 votes for C then B then A

By: novalis

novalis — Tue, 02 Mar 2004 17:52:54 +0000

Dave, what’s wrong with Python? (ooh, let’s have a programming language flame war to go with our voting system war ;) I’m not set on Condorcet (I prefer the simplicity of approval voting). But I don’t think it’s hard to understand—I learned about it in 9th grade, IIRC.

By: Dave

Dave — Tue, 02 Mar 2004 07:03:35 +0000

I have no problem with preferential voting systems, though I think they introduce strategies for voters which are to some extent counter-intuitive. It does bother me if a candidate wins because his or her supporters understand voting strategy better, rather than that candidate having the most popular support.

By: John Quiggin

John Quiggin — Tue, 02 Mar 2004 05:55:37 +0000

As noted in my previous post, Australians and Irish (not famously intellectual groups of voters) have no trouble with preferential voting systems, of which Condorcet is an example. But I agree with your scepticism about Condorcet.

By: Dave

Dave — Tue, 02 Mar 2004 05:52:18 +0000

The main problem with Condorcet is that it’s hard for the “average joe” to understand. I know these people have an argument about why it’s not, but any algorithm that requires college math isn’t going to appeal to a national populace. I also tend to be wary of arguments like “Condorcet is the best because it is the only method which satisfies the Condorcet Criterion and four other criteria based on it.” The fact that they have an implementation in Python of all things scares me too. I prefer approval voting to any of the other methods. My second preference is plurality, since it is simplest, but plurality wouldn’t work well in a country with a broader political spectrum than the U.S.

By: novalis

novalis — Mon, 01 Mar 2004 23:59:03 +0000

Then, as stated in the critique above, the optimal choice for C’s supporters is to vote strategically for B, so that B finishes the first round ahead of C. But, because polling is inexact at best, it’s impossible to determine when to switch from CBA to BCA. Personally, I’m a fan of approval voting, because of its simplicity. I understand that it (like all other systems) has its problems. I recently participated in an election (for a small science fiction association). We did sequential (non-instant) run-offs, and the importance of non-primary choices became quite clear. In straw polls, candidates A and B had wide first-tier support. I asked for second choices, and candidate C swept the 2nd votes. Once everyone saw this, C ended up being elected.

By: Conrad barwa

Conrad barwa — Mon, 01 Mar 2004 23:48:22 +0000

Taking this a bit further it seems likely that, whatever rule is chosen for resolving cycles, an implementable Condorcet system would be vulnerable to exploitation by strategic choices to run (or not run) particular candidates whose function would be to tip the balance in favor of some other candidate. Possible solution in this case might be to impose stringent conditions for entry into the electoral race –either via some sort of financial yardstick (from individual donors) or some other indicator of a critical level of popular support not restricted to a narrow constituency; to weed out such candidates. Though this has problems in itself.