[EM] Truncation

[Adam Tarr]

Joe Weinstein wrote:

>There is no point in invalidating or penalizing ballots of voters who have 
>reason to lack perfect information (especially when there is a gaggle of 
>mostly unknown candidates), or who do have (for their purposes) perfect 
>information but are simply trying to minimize time and effort and 
>confusion in marking their ballots.   Rather, when a given candidate has 
>not been explicitly marked, he can still be given a default evaluation.

I think virtually everyone agrees with this.  The debate is not really 
whether we ALLOW truncation in ballots.  The debate, rather, is what 
strategic impact truncation has in various voting systems, and what sort of 
incentives that gives to the voter.

Recently, there has been a revival of the debate about margins-based 
Condorcet completion methods versus winning votes-based Condorcet 
completion methods, with an eye towards the effects of truncation on 
each.  Specifically, there is the remarkable fact that a voter in a winning 
votes-based Condorcet voting system can NEVER be hurt by fully expressing 
their preferences.  There are cases where fully voting your preferences can 
fail to help you, but it can never actually hurt you.

This is not a distinction without a difference.  In every other ranked 
balloting method I am familiar with, the voter could potentially look at 
the results of an election and say, "If only I (and others like me) had 
just left some information off the bottom of our ballot, without changing 
the order of any candidates above that point, then I could have gotten a 
better result."  This is not the case in winning votes-based Condorcet 
methods, and that's an incredibly powerful statement.

One of Donald Davidson's favorite criticisms of non-IRV alternative voting 
methods is that, "your vote for your second choice can help defeat your 
first choice." (paraphrasing).  This is simply not true in winning 
votes-based Condorcet methods.  It is true, however, in margins-based 
Condorcet voting, or in Borda count, or in cardinal rankings, or in 
approval voting.  IRV itself is immune to this criticism, but in IRV your 
first place vote can help defeat your second place vote (and give the 
election to someone else altogether), which is not really any better.

So winning votes-based Condorcet voting's resistance to strategic 
truncation is essentially unparalleled in voting systems.  Blake has argued 
that this could encourage voters who sincerely have no preference among 
lower candidates to randomly rank those candidates on the bottom of their 
ballot, since it can't hurt them to do so.  This is of course true, but in 
my mind it is an extremely minor issue - we're talking about candidates who 
are so minor that the voter doesn't care enough to form any opinion on 
them.  If the voter is strategically aware of the advantage of full 
ranking, they are probably savvy enough to spend a few minutes reading 
basic candidate statements and picking some order to put the candidates 
in.  And in the end, doesn't it make sense to reward the voter who puts 
more information on their ballot rather than the voter who puts less?

There's no way to distinguish between the lazy voter and the sincerely 
indifferent voter, or between the informed voter and the haphazard 
voter.  But I'd rather put the haphazard voter on nearly the same ground as 
the informed voter than penalize the informed voter vis-a-vis the lazy 
voter.  Especially when doing otherwise gives rise to the strategically 
lazy voter, which is a FAR more dangerous development than the 
strategically haphazard voter.  This is not just a philosophical debate; 
I've shown examples in recent threads where margins-based Condorcet allows 
seemingly undemocratic results due to truncation.  I haven't seen any 
counter-examples where winning votes comes up with the undemocratic result 
due to its failure to penalize full preferences.

>Forest notes that the usual American academic grading system - which has 
>the advantage of being very familiar to almost all Americans - allows the 
>six grades A-E.  Typically,  grades A-D are degrees of definite pass, 
>grade F is definite fail, and grade E indicates that information is 
>incomplete to infer a definite pass or definite fail.
>
>Accordingly Forest proposes that if a given election is to be run so as to 
>allow voters to use at least four grades, then a good approach would be to 
>allow use precisely of the six academic grades, with ungraded candidates 
>being awarded the default grade E.
>
>This proposal makes excellent sense.  Four levels are surely enough to 
>distinguish substantially distinct degrees of active approval.  One level 
>suffices to express active disapproval.

At first I didn't like this idea, but its grown on me.  The simplicity to 
the voter of ABCD(E)F voting is worth it.  The voters who are interested 
and involved enough to actually need six distinct levels of approval are 
the same voters who will understand that the unmarked candidate will get 
the E grade.

I spent some time a few months back seeing if approval-completed Condorcet 
could be made to work using this sort of ballot, but in the end I realized 
that the only time approval completion worked like I thought it should was 
when the approval votes supported the sincere Condorcet winner.  When the 
approval votes did not do so, the system encouraged all sorts of strategic 
manipulations.  So I gave up on ACC, and I now hang my hat with 
winning-votes based Condorcet, which seems to be the system that is most 
resistant to strategic manipulation by a wide margin.

-Adam


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