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While I would certainly be more happy in a world with either IRV or Condorcet method than FPTP, I think this argument against IRV is too simplistic. The situat

While I would certainly be more happy in a world with either IRV or Condorcet method than FPTP, I think this argument against IRV is too simplistic. The situation is candidates D, R with the largest numbers of voters who prefer them first, and consensus candidate I with smaller first preference than D, R but lots of 2nd preference. Under any Condorcet method, the D and R voters can hurt their candidate by ranking I as second (later-no-harm criterion). This leads to a negative partisanship spiral, say, as D/R voters feel like they must only rank 1 candidate in order to counter the threat from the other party doing the same, and thus the consensus candidate I, which would be the Condorcet winner under voter's true preferences, does not become the winner under the actual votes. IRV does a better job of inducing everyone to rank choices.

ClayShentrup 8y ago
The Later-no-harm criterion is basically a nonsensical idea invented to make IRV look better than it is. See a Princeton math PhD dissect it here. http://scorevoting.net/LNH http://scorevoting.net/LNH tl;dr for non-experts (I co-founded the Center for Election Science and have studied voting methods since 2006). The idea behind LNH is that if I vote for the Green in 1st place, it's "safe" to then rank the Democrat 2nd, because that can't cause the Democrat to defeat the Green. See this explained visually in this video by Andy Jennings, another CES co-founder who did his math PhD thesis on voting methods. http://www.youtube.com/watch?v=JtKAScORevQ http://www.youtube.com/watch?v=JtKAScORevQ The Later-no-harm criterion is highly misleading, because "safe" here means safe for the CANDIDATE. But tactical voting is about what's good for the VOTER, not the candidate. With IRV, the Green voter's best strategy is to actually rank the Democrat in 1st place. So the whole notion that he can safely rank the Democrat #2 after he's ranked the Green #1 starts with a false premise. If he's rational, he WILL NOT rank the Green #1. It's the same reasoning that Democratic primary voters have about far left candidates. Even if you win the nomination and advance to the general, you're so far left that you'll probably lose against the Republican, by not capturing enough of the center of the electorate. Approval Voting actually makes it safe to ALWAYS vote your favorite. And, in general, to vote for everyone you prefer to your favorite of the frontrunners.
- jsmith45 8y ago
  Doesn't later-no-harm only fail on condorcet methods if there is no Condorcet winner? From what I've seen of most Condorcet methods, the best way to tactically vote differs if there is or is not a Condorcet winner, and often become a major mistake in the other circumstance. Basically it means unless you know what the results will be tactical voting will have a rather good chance of backfiring on you, making it not worthwhile, which seems like a good thing to me.

ClayShentrup 8y ago

The Later-no-harm criterion is basically a nonsensical idea invented to make IRV look better than it is. See a Princeton math PhD dissect it here. http://scorevoting.net/LNH http://scorevoting.net/LNH tl;dr for non-experts (I co-founded the Center for Election Science and have studied voting methods since 2006). The idea behind LNH is that if I vote for the Green in 1st place, it's "safe" to then rank the Democrat 2nd, because that can't cause the Democrat to defeat the Green. See this explained visually in this video by Andy Jennings, another CES co-founder who did his math PhD thesis on voting methods. http://www.youtube.com/watch?v=JtKAScORevQ http://www.youtube.com/watch?v=JtKAScORevQ The Later-no-harm criterion is highly misleading, because "safe" here means safe for the CANDIDATE. But tactical voting is about what's good for the VOTER, not the candidate. With IRV, the Green voter's best strategy is to actually rank the Democrat in 1st place. So the whole notion that he can safely rank the Democrat #2 after he's ranked the Green #1 starts with a false premise. If he's rational, he WILL NOT rank the Green #1. It's the same reasoning that Democratic primary voters have about far left candidates. Even if you win the nomination and advance to the general, you're so far left that you'll probably lose against the Republican, by not capturing enough of the center of the electorate. Approval Voting actually makes it safe to ALWAYS vote your favorite. And, in general, to vote for everyone you prefer to your favorite of the frontrunners.

jsmith45 8y ago
Doesn't later-no-harm only fail on condorcet methods if there is no Condorcet winner? From what I've seen of most Condorcet methods, the best way to tactically vote differs if there is or is not a Condorcet winner, and often become a major mistake in the other circumstance. Basically it means unless you know what the results will be tactical voting will have a rather good chance of backfiring on you, making it not worthwhile, which seems like a good thing to me.