[EM] Range strategy pathological example (was Re: IRV vs Plurality)

[Jonathan Lundell]

On Jan 26, 2010, at 10:30 PM, Jameson Quinn wrote:

> 
> Two weaknesses, it seems to me, and I'm less sanguine about their fixability.
> 
> Depends what you mean, of course. But I stand by my "one fixable weakness".
>  
> 
> One is, as you suggest, the strategy problem. Range, and it's limit in one direction, approval, require the voter to make cast a strategic vote; there really isn't any such thing as a non-strategic range or approval ballot. But voters are privy to different amounts of variably useful information about other voters' preferences, and other voters' strategic choices in view of those (perceived) preferences, and so on ad infinitum.
> 
> Yes. There are two ways to fix this. One is to do something to "idiot-proof" the ballots - allow only near-top or near-bottom votes, or encourage middle votes only for lesser-known candidates. This essentially make Range into almost Approval, without losing too much expressivity (and thus no one is forced to vote unstrategically simply to gain expressivity). As you say, there's still strategy, but I think voters could handle it.

That goes to Juho's reply, to which I'll respond here. He said:

> If Range becomes Approval like then you might add also the weaknesses of Approval in your list.


My objection to Range as requiring a strategic vote applies to Approval as well. The strategy is (potentially) simpler to describe, but it still can be executed well or poorly or naively, and for success it depends on how well the voter can predict both the preferences and the strategies and counter-strategies of the other voters.

> 
> The other way is to try to have the system handle the strategy for the voters. There are several possibilities - I've proposed "Score DSV", another possibility is to do a hybrid Bucklin system with IRV-like sequential "elimination" (actually, non-elimination vote spreading). You may say that these systems are no longer truly range-like (they do satisfy the Condorcet criterion, and they are not trivially precinct-summable, so you'd have a point), but they do still encourage range-like or approval-like voting.
>  
> The second problem kicks in with the suggestion that there *is* a sincere range ballot (not that any voter would cast it), namely some objective measure of utility, comparable from voter to voter. The idea that there's some objective (or at least intersubjective) common measure of cardinal utility is, deservedly, a fringe idea—at best—in social choice theory.
> 
> 
> It doesn't have to be objective or intersubjective (or cardinal, for that matter). It just has to be subjectively interval-scaled, or decently close to interval-scaled. Which may not be exactly true, but is IMO certainly close enough to truth to run with. So I don't think this is an insurmountable problem at all.

I don't really agree, though perhaps we can focus on the strategy problem for not. The substance of my disagreement is again twofold, one being that as a voter, I don't have any idea of what the scale is. Translating a list of 30 policy statements, of more or--probably--less credibility into a numeric value is something I don't know how to do. The second is the comparability of my scale to other voters.

This problem is independent of strategy. If, by some miracle, we could come up with some sincere and objective utility rating of each voter for each candidate, then it'd be trivial to maximize some utility aggregation function (though we'd no doubt have an argument about how best to aggregate). But those ratings, for all practical purposes, don't exist. So I'm content to focus on the strategy problem.

> 
> Jameson Quinn


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