The EM vote on single-winner methods

[Steve Eppley]

Marcus G asked:
>In elections for the Australian House of Representatives and all
>State Lower Houses bar Qld and Tasmania, we use Compulsory
>Prefential Voting (often "CPV")  ie failure to allocate a
>preference to all candidates invalidates the vote. In elections for
>Queensland's unicameral parliament  we use Optional Preferential
>Voting ("OPV") - you can truncate at any point. Does the MPV system
>discussed on this list compel the allocation of preferences?

No.  None of the ranked balloting systems discussed here invalidate
ballots due to truncation.  Candidates omitted from the rankings are
treated as though the voter had ranked them equally last.  

For example, in an election between candidates A, B, and C, the
ballot {B} would be treated identically as the ballot 
   B > A=C=D=E=F=...
(Candidates D, E, F, etc., were write-in candidates on some other
voters' ballots.)

We've also considered a slight improvement.  Allow the voters to
rank some detested candidates below the unranked:

   preferred_candidates > unranked_candidates > despised_ candidates

Assuming this wouldn't complicate things too much for the voters, I 
think all of us here would probably prefer adding this option.

The STV multiwinner system for prop rep has several variations. 
None of them invalidate truncated ballots, but truncated ballots may
be partially or entirely "wasted".  It depends on the fraction of other 
voters' ballots which get transferred away from winners who have an 
excess.

---Steve     (Steve Eppley    seppley at alumni.caltech.edu)