Margins Example Continued

David Marsay djmarsay at
Mon Sep 21 05:30:52 PDT 1998

I've come back to an interesting thread:

> From:          Mike Ositoff <ntk at>
> Subject:       Margins Example Continued

The debate is between 'margins' and 'votes-against' in variations of 
Condorcet, who does not explicitly deal with tied rankings. The 
differences cited so far concern tactical voting.

I suggest that we consider tactical voting in the particular case 
where one has spatial voting. This is often used in voting theory. In 
the simplest case one has a left/right scale. Voters have views along 
this scale, and candidates take positions along the scale. Voters, we 
suppose, never rank a candidate below candidates who are 'more 

It is well known that one cannot avoid tactical voting in the general 
case. I consider 'tactical spatial voting', where the voter's 
true preferences are spatial, but their declared preferences may not 
be. I claim that Condorcet with the 'margins' interpretation 
(e.g., see:
>From:             Norman Petry <npetry at>
>Subject:          Re: Schulze Method - Simpler Definition
is immune to tactical spatial voting. My tentative proof relies on the 
following observation:

If x <a y and y <b z (where x,y,z are candidates and  a,b are the 
'margins') then x < c z, where c >= min{a,b}.

The proof is done by cases, over the possible spatial relationships 
between x, y and z. Incidentally, this shows that the only Condorcet 
cycles one can have are indifferences.

Being able to say that 'Condorcet/margins' copes well with spatial 
voting seems to me to a big plus for 'margins'. Is the same true for 

Sorry folks, but apparently I have to do this. :-(
The views expressed above are entirely those of the writer
and do not represent the views, policy or understanding of
any other person or official body.

More information about the Election-Methods mailing list