[EM] voter strat & 2-party domination under Condorcet voting

[James Gilmour]

> > In a message dated 8/13/05, Warren Smith writes: 
> >>Given that this is the case, we now can take it to be 100% certain that
> >>Condorcet voting methods will lead to 2-party domination,  just like the 
> >>flawed plurality system those methods were supposed to "fix", and just
> >>like experimentally is true with IRV.
> > 
> RLSuter at aol.com wrote:
> > I just can't buy this. It's not even 100% certain that plurality 
> > voting methods will lead to 2-party domination.

I think you need to specify a lot more of the political context before you can make assertions like these about any
voting system.  It is probably also relevant to distinguish between true single-winner elections (eg state governor,
city mayor) and single-member district elections for representative bodies like state legislature or city council.  But
even then, the true single-winner elections do not take place in isolation from the "representative" elections.  In the
US, the system is a mixture of both, but maybe the single-winner elections, especially for President, have a dominating
effect on the whole scene.

In the UK we have only single-member district elections for the most important UK public election, ie electing MPs to
the UK Parliament at Westminster (London).  For past 50 years all MPs have been elected by FPTP (plurality) in
single-member districts. (The overwhelming majority have been elected from single-member districts for 100 years).  Over
this period party fortunes have waxed and waned, but we certainly don't have "two-party politics" and haven't had that
for some time, at least not as measured by shares of the votes.

In England there are currently three significant parties: Conservative 35.7%; Labour 35.5%; Liberal Democrats 22.9%;
several others 5.9%.  In Scotland there are currently four significant parties: Labour 39.5%; Liberal Democrats 22.6%;
Scottish National Party 17.7%; Conservative 15.8%; several others 4.4%.  Of course, the defects of FPTP have tended to
turn these voting patterns into results that could be described as "two-party domination" in terms of seats won,
especially in England.  It is a real change, however, because the share of the votes UK-wide that were cast for the two
leading parties (Labour and Conservative) in UK general elections has declined from 97% in 1951 and 96% in 1955.  And
the voting system for the UK Parliament hasn't been changed during the past 50 years.
James Gilmour