# Consensus?: IRV vs. Primary w/Runoff

Steve Barney barnes992001 at yahoo.com
Thu Jan 31 15:53:31 PST 2002

```Forest and "DEMOREP1 at aol.com":

Yes, all voting methods certainly are manipulatable. In fact, that was
mathematically proven by Gibbard and Satterthwaite (Satterthwaite, Mark A.;
"Strategyproofness and Arrow's Conditions: Existence and Correspondence
Theorems for Voting Procedures and Social Welfare Functions"; Journal of
Economic Theory; Vol. 10, No. 2; April, 1975; 187-217; #654). However, it
remains true that some methods are more manipulatable than others. I am only
claiming that IRV is LESS manipulatable than the primary w/runoff procedure
when there are 4 or more candidates. With 3 candidates, given that voters
sincere preferences do not change from one balloting to the next, they are
mathematically equivalent; that is, they yield the same results. Does anybody
know if a proof of this assertion, or something to the contrary, has been
published? How about an example showing a case where the IRV is more
manipulatable than the Plurality Primary w/Runoff.

SB

> Date: Thu, 31 Jan 2002 02:23:24 EST
> From: DEMOREP1 at aol.com
> To: election-methods-list at eskimo.com
> Subject: Re: Consensus?: IRV vs. Primary w/Runoff
>
> Forest wrote-
>
> All seriously proposed election methods are subject to manipulation,
> because all require strategy to one degree or another to maximize expected
> outcome, and all optimal strategies require information about the
> intentions of the other players.
>
> -----
> D- Again -- his happens when there are 3 or more choices.
>
> N1 AB
> N2 BA
>
>
> C may (depending on the method being used) --
>
> beat A and B
> beat A lose to B
> beat B lose to A
> lose to both A and B
>
> More combinations, of course, with 4 or more choices.

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