[EM] PR in student government

[James Gilmour]

> Abd ul-Rahman Lomax> Sent: 17 April 2007 15:50

Just two points to which I wish to respond.

> The ballots could also be counted sequentially, as needed. I dislike 
> this, because I think every vote should be counted, even if 
> supposedly "moot." If I went to the trouble to cast it, it shouldn't 
> be tossed in the trash!

This is an understandable "social choice" interpretation of ALL the
information on ALL the ballot papers.  But that is not what STV-PR is
about, and certainly not where it came from.  You vote for your first
choice.  Your second preference is a contingency choice, to be brought
into play only if your first choice is already elected and cannot
proportionately represent you as well, or has so little support that
he/she has no prospect of election and is excluded (eliminated).  And so
on.  And of course, originally it was "your vote", i.e. your whole vote,
that was transferred.


> If I was a candidate for office, and it turns out that many people 
> voted for me, but not at a high enough preference for me to be 
> elected, I'd hate not to know this! The result might actually be 
> encouraging. Or not, depending on what is in those buried votes....

The problem of excluding a "Condorcet winner" is unavoidable in STV-PR
so long as we give an absolute undertaking to every voter that under no
circumstances can a lower preference count against a higher preference.
Most proponents of STV-PR regard that undertaking as extremely
important, and that view is, in my experience, shared by the
overwhelming majority of the electors with whom I have ever discussed
STV.  Once you change that solemn undertaking to save a "Condorcet
winner" from exclusion, you open the door to tactical voting which is
otherwise impossible in real STV public elections, i.e. with large
numbers of electors whose preference patterns you cannot possibly know.
This exclusion rule makes STV-PR non-monotonic, but that is not
generally regarded as important and certainly nothing like so important
as ensuring that a lower preference can never count against a higher
preference.  Also, the non-monotonic effect cannot be exploited by
either the candidates or the voters, so it is of no practical effect.
It would be nice, but we cannot have it all  -  at least, not all at
once!!
James Gilmour