[EM] IRV vs Plurality

[Juho]

On Jan 10, 2010, at 1:21 AM, Jameson Quinn wrote:

>
>
> 2010/1/8 Kevin Venzke <stepjak at yahoo.fr>
> Hi Dave,
>
> --- En date de : Ven 8.1.10, Dave Ketchum <davek at clarityconnect.com>  
> a écrit :
> > I said "approval", not
> > "Approval".  I read Range ratings of A-1, B-9, and C-2
> > as saying B is much more strongly approved than A or B.
>
> You are looking at the meaning of Range ratings on a ballot, but you
> don't seem to care how Range uses this information. That's what I'm
> talking about.
>
> Kevin Venzke
>
>
> If I understand you correctly, I think that this is an important  
> point, and should be expressed more clearly. It is, in my opinion,  
> one of the ONLY valid arguments against Range, and yet it is (again,  
> my opinion only) in some cases a telling one.
>
> The point is that Range encourages naive voters to vote non- 
> strategically. If even sophisticated people like Ketchum's can laud  
> range ballots' expressivity, without noting that strategy could  
> limit this expressivity, we can imagine voters, often far less  
> sophisticated, will fail to understand range strategy at all. Some  
> voters will, strategically, vote approval-style, and other voters  
> will NOT.
>
> A range proponent might argue that this just means that Range will,  
> in practice, perform somewhere between the (excellent) theoretical  
> Range result and the (pretty good) theoretical Approval result.  
> Indeed, simulations show that, for any randomly distributed constant  
> proportion of strategic voters, Range performs well, and in fact  
> outperforms most other methods (including Condorcet methods) given  
> the same proportion of strategic voters. However, this argument  
> assumes random distribution. Such an assumption is not only  
> unjustified in the typical election; in fact, there are grounds for  
> assuming the contrary. Voting groups are, by definition,  
> ideologically distinct, and thus there is every possibility for  
> their propensity for strategic voting to be distinct. If groups do  
> thus vote strategically at different rates, Range can give seriously  
> deficient results - with sufficient strategy gap, even the worst  
> candidate can win. (Condorcet methods, on the other hand, will tend  
> to still elect the Condorcet winner despite any strategy, unless  
> results are close and/or some voters use a specifically misguided  
> strategy).

Yes. Another way to describe this situation is to say that strategic  
voting pays off. A voter/party that uses strategy is more likely to  
win than one that votes sincerely. For many that is a good enough  
reason to vote strategically. And when many do, also the hesitant ones  
may follow.

>
> I think it would behoove Range advocates to think about these  
> issues, because one horror story of this kind could be more  
> obviously unfair than many of the worst pathologies of other systems.
>
> However, there are forms of Range voting which would avoid this  
> problem. Most obviously, there is Approval itself, which is  
> technically a form of Range. That can be extended to any version of  
> Range which disallows or strongly discourages most "weak" votes. For  
> instance, there could be options to vote only 0 ("worst"), 1("bad"),  
> 50 ("intriguing"), 99 ("better"), and 100 ("best"). 50 is labeled as  
> "intriguing" because the option is intended particularly for little- 
> known candidates whom a voter believes, but is not sure, deserve  
> support, not for well-known candidates who are simply of average  
> quality. This would give additional expressiveness beyond Approval,  
> without a significant risk of pathological situations where a  
> strategic minority imposed their will over an unstrategic majority.  
> For instance: in a standard "two frontrunner" scenario, where no  
> voter was uninformed about either of the frontrunners and so nobody  
> rated either as merely "intriguing", such a system could not give  
> the "wrong" strategic-plurality winner unless the gap were less than  
> 1% (ie, closer than 49.5%-50.5% of the two-way vote).

In practice it might however make sense to rate the two frontrunners  
strictly at 0 and 100. Elections are often tight and therefore also  
smaller differences than 49.5%-50.5% may be crucial / quite often  
decide which one of the frontrunners will win. This approach would  
mean that all other ratings (1, 50, 99 and others) would be reserved  
for giving sincere opinions on candidates that can not win.

(There could be also strategic thoughts on what will happen in the  
next elections to these candidates and their parties. This kind of  
future related considerations could lead to using only values 0 and  
100 also for all those candidates whose support level one wants to  
influence (although they can not win this time).)

Juho


>
> Jameson Quinn
> ----
> Election-Methods mailing list - see http://electorama.com/em for  
> list info

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