Margins -- Blake is right -- slight amplification (fwd)

Blake Cretney bcretney at
Tue Sep 29 15:19:38 PDT 1998

On Sun, 27 Sep 1998 20:24:19   Mike Ositoff wrote:
>> > Hugh R. Tobin wrote:
>> > 
>> > > I agree that votes-against does not permit a rational "defensive"
>> > > strategy of truncation; moreover I remain to be convinced that in
>> Not sure what you mean by that; defensive truncation, in VA, makes
>> it impossible to profit by voting an insincere preference, and
>> penalizes order-reversal.
However, if you guess wrong, and you are not the CW, it lowers your
chance of winning.  It never increases your chance of winning.  The
order reversal strategy, however, can actually defeat an order-reversal
campaign by saving your candidate, as opposed to getting a third 
candidate elected.  For this reason I do not consider the truncation defensive strategy to be rational, and therefore a more effective
deterrent than order-reversal.
>> > > margins  it would ever be rational for a voter to truncate, but not to
>> > > reverse order.  
>> > 
>> > It may not have been clear enough that the second point relates to a
>> > separate issue from the first, that is, a charge made on this list that
>> > the margins tiebreak allows an "offensive" truncation strategy, which
>> > fails in "votes against".  Such a strategy has no independent
>> > significance because it is only a weaker alternative to order-reversal
>> > strategy, which in the right conditions can work under both methods.
>> No, truncation has independent significance because it occurs in
>> all rank-balloting elections, and will surely be common in public
>> elections. Margins is vulnerable to it, and VA isn't.
All voters who know how Votes-Against works will use the random-fill
strategy instead of sincerely or insincerely leaving candidates unranked.

Of course, if a system penalizes voters for leaving candidates unranked,
doing so will not play a role in successful strategy.  However, those
voters who catch on to random-fill will not be affected by the penalty.
In aggregate, there votes will be scored as if they were using Margins.
>> To say that truncation isn't significant because the would-be
>> truncator could order-reverse instead in VA is like saying that
>> door-locks are useless because the burglar could instead saw a
>> hole in the door. It's more trouble, and it carries a great risk.
If you prefer B to C, but truncate, you do so because you hope to
create a large win against B.  The more effective way to do this
is to actually rank C over B.  Of course, this goal may turn out to
be undesirable, if it makes C win over all.  However it makes no
sense to only half pursue defeating B because you are not sure
if it is desirable to do so or not.

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