[EM] Why I prefer ranked-choice voting to approval voting

[Toby Pereira]

Sorry - in a two-round system, it's clear that it might be advantageous to vote for a candidate other than your favourite in the first round. It's not so intuitively clear that it might be to your advantage not to rank your favourite candidate top in IRV.

 
      From: Toby Pereira <tdp201b at yahoo.co.uk>
 To: Jameson Quinn <jameson.quinn at gmail.com>; Jeff O'Neill <jeff.oneill at opavote.com> 
Cc: election-methods <election-methods at electorama.com>
 Sent: Sunday, 16 October 2016, 11:29
 Subject: Re: [EM] Why I prefer ranked-choice voting to approval voting
   
The French presidential election isn't IRV though is it? It's just a two-round system - https://en.wikipedia.org/wiki/French_presidential_election,_2012 In such an election it's much clearer that you might not want to vote for your favourite in the second round than in IRV.
But Jameson, I think your centre squeeze illustration is a good one. I've seen many people (mainly on the Center for Election Science forum) saying that IRV is bad because there are situations where voting for your favourite results in a worse outcome for you, but without an explanation for the mechanism, and when and why anyone might know when not to rank their favourite top.
So as I understand it, you've got three candidates: L, C and R - C is the Condorcet winner. Someone's preference order might be L>C>R, but by submitting that ranking, C gets eliminated first and L could then lose to R in the run-off. But by ranking C first, C would be a sure winner over R in a run-off, so it's a safer vote, especially if your main priority is for R not to get elected.


 
      From: Jameson Quinn <jameson.quinn at gmail.com>
 To: Jeff O'Neill <jeff.oneill at opavote.com> 
Cc: election-methods <election-methods at electorama.com>
 Sent: Saturday, 15 October 2016, 14:29
 Subject: Re: [EM] Why I prefer ranked-choice voting to approval voting
  




But there's an important, and predictable, class of election scenarios where it's strategically crucial NOT to rank your favorite first: center squeeze scenarios. If you have two candidates at ideological opposite points, with a third candidate in the middle near the median voter, it is actually quite common for the center to have the lowest first-choice support and get prematurely eliminated. This kind of thing happened in Burlington 2009; in multiple recent French elections; tragically, in Egypt 2011; and would have happened in the US 2000 if Nader had gotten over 25%. In this case, the correct strategy for one group of voters is to rank their true first choice in second place. Understanding this, and correctly seeing when it applies, is a HUGE cognitive burden for IRV voters.
 When you say that "it is actually quite common for the center to have the lowest first-choice support and get prematurely eliminated," we need to clarify "quite common."  If you mean 5-10% of the time, then I could believe that, but if you mean 50% of the time, then I would disagree.  It would be really interesting if a statistician could collect the data and present results.

Depends on various factors, but generally I'd put it in the 10%-50% range. It's happened in 2 of the last 4 French presidential elections so 50% is not a crazy estimate. 



   
 

   
 
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