Thanks Peter for your comments >Suppose that by my estimation about the electorate is about
>400: Smith, Jones, Johnson >300: Jones, Smith, Johnson >600: Johnson, Jones, Smith Johnson loses regardless as to whether Smith or Jones is eliminated Normal IRV with no strategy: Jones is eliminated in the first round and Smith wins in the second round. IRV with a strategy, of 101 vote switch, from Johnson voters to Jones Smith is eliminated in the first round and Jones wins in the second round. The Johnson voters would have to except Jones as their second best choice. A more realistic example is the following: 340: Smith, Jones, Johnson 40 Smith, Johnson, Jones 280: Jones, Smith, Johnson 20: Jones, Johnson, Smith 620: Johnson, Jones, Smith First let's look at a primary with a top two general election: Smith (380) and Johnson (620) advance and Jones is eliminated (with 300) Assume the Jones voters vote their same preference in the general election. Smith wins (660) and Johnson loses (640) Assume that 100 of the Johnson voters vote for Jones in the primary Jones (400) and Johnson (520) advance to the general election, and Smith is eliminate (380) Assume the Smith voters vote the same preference in the general election. Also assume the 100 who voted for Jones in the primary switch back to Johnson in the general election. Johnson wins (with 660) and Jones loses (with 640). The Strategy worked. It is clear that a primary (a plurality election) and a top two run-off general election taken together is subject to Strategic voting. The primary may be non-monotonic as well as the general election but together they are monotonic. Next let's look at an IRV election: In the first round Smith (380) and Johnson (620) and Jones is eliminated (with 300) Assume the Jones voters vote the same preference in the general election. Then in the second round Smith wins (660) and Johnson loses (640) Assume that 100 of the 620 Johnson voters change their preference to the following 100: Jones, Johnson, Smith 520: Johnson, Jones, Smith Jones (400) and Johnson (520) advance to the second round, and Smith is eliminate (380) Now under IRV rules the 100 who voted for Jones continue to vote for Jones. Jones wins (with 740) and Johnson loses (with 560). The Strategy did not get Johnson elected but Johnson votes would be happier it Jones than Smith. IRV elections are LESS subject of strategic voting than a primary and a top-two run-off. Both voting systems are clearly monotonic. Why is Monotonicity an issue, if they are both systems are monotonic and monotonic is not ever a constitution requirement. ---- Election-Methods mailing list - see http://electorama.com/em for list info
