[EM] IRV vs Plurality

[Jonathan Lundell]

On Jan 10, 2010, at 11:22 AM, Terry Bouricius wrote:

> Although Abd often asserts that IRV replicates FPTP results, I don't think 
> he is claiming that in the last Burlington election. The plurality leader 
> was the Republican Kurt Wright with 33%. He presumably would have won 
> under FPTP. However, as the weaker candidates were eliminated (first the 
> Green and Independent, and then the Democrat) the Progressive Party 
> incumbent mayor who was in second place in the initial first-choice tally 
> won the runoff.
> 
> Of course, there is the additional factor that a change in voting rules 
> would likely change both campaign tactics as well as fears about spoilers, 
> and whether all five candidates would have even run. It is certainly 
> possible that the Democratic Party candidate would be dismissed as a 
> "spoiler" with the Republican challenger and Progressive incumbent being 
> seen as the "credible" candidates. It is also quite possible that the 
> Independent with around 10% first choice support would not have run if 
> FPTP had been used. Voters rather universally ranked their true favorite 
> choice as number one, but that wouldn't have been true under FPTP.
> 
> IRV resulted in a VERY different set of dynamics than would have existed 
> with FPTP, so it is impossible to say with any certainty what the outcome 
> would have been. It is also noteworthy that the current debate is NOT 
> about substituting typical FPTP, but rather FPTP with a 40% requirement. 
> Under that scenario, it is quite likely that the Progressive would have 
> won as well, since no candidate reached 40% initially, and IRV replicated 
> the likely runoff outcome.
> 

This is a point that bears repeating, since it doesn't seem to sink in. It's much to easy to casually assume that ballots cast under one system (in this case IRV) can be recounted under some other rule with the assumption that voters would have cast the same (or at least equivalent) ballots under that other rule.