View source for Talk:Later-no-help criterion

== Failing Later-no-help in IRV ==

As discussed in the Favorite Betrayal Criterion, my improvement to IRV makes favorite betrayal unnecessary but apparently it will now violate later-no-help.

12 A

8 B>A

6 C>B

IRV and my “improved” IRV elects B.

When 3 voters change their ballots: IRV still elects B. My “improved” IRV changes the result into a paradoxical tie.

9 A

3 A>C

8 B>C

6 C>B

When three supporters of A add the preference C, the probability of electing A has increased. A goes from a total defeat to a small chance. By definition, I believe this violates later-no-help. Frankly, I don’t see that as bad when the intent is to help the candidate being added to the ballot.

If the voter’s intention is to help C because there really is a preference over B, then this change is sincere. That’s well worth creating a tie in which this voter’s candidates of choice have two thirds of a chance to win. It’s later-some-help.

If these voters were replacing A>B (their sincere choice) with A>C, then it’s a tactical move to make the result into a tie when it isn’t there. I can see a candidate wanting to do that, but not a voter. Before changing, these voters were hoping for A or B, and they got B (having indicated they didn’t want C). After the change, they are getting A or B or C. Why choose a one third chance of losing completely when you already have a guarantee it won’t?
[[User:RalphInOttawa|RalphInOttawa]] ([[User talk:RalphInOttawa|talk]]) 14:10, 20 December 2023 (UTC)