>The only large-scale demonstration of IRV we have is Australia's lower
>>house, where district elections are virtually all bipartisan (there are
>>apparently three parties represented in the legislature, but only two of
>>the three are prominent in any given district). This in spite of the
>>fact that Australia has a strong multi-party system fed by proportional
>>representation in its upper house 

More than just Australia's lower house (House of Representatives).  IRV is used in state elections and local government elections.

The essential information to be gained is that IRV delivers stable, two-party dominated legislatures, noting that one "party" may formally exist as multiple parties in tight cooperation (eg liberal/national).

>
>For an example of a three party IRV election ( the Queensland state election of 1998 where Pauline Hanson's anti-immigrant One Nation Party challenged the Labour party and Liberal/National coalition ) visit Adam Carr's Electoral Archive:
>
>http://psephos.adam-carr.net/countries/a/australia/states/qldindex.shtml
>
Hansons' "One Nation" examples are not particularly good, except for examples of the strategy of two of three strong candidates agreeing to "exchange preferences" (advise supporters to rank the other second).
Hanson was an ejected radical member of the liberal party, ejected just weeks before her election.  There is too much sensationalism involved in every One Nation story for it to be a clear example of anything.

A better example is Janine Haines' attempt to win the lower house seat of Kingston, South Australia, in 1990.  Haines was a federal senator from South Australia and the leader of the centrist party, The Australian Democrats.  Her failure to win is a clear example of how IRV makes it hard for a centrist candidate, a clear condorcet winner with a significant primary (1st preference) vote, to overcome the two dominant parties.

______________________________________

Digressing to PR....

>12 out of 76 members of the Australian Senate belong to parties other than National, Liberal or Labour.

NB.  At this level of analysis, National and Liberal can be considered to be factions of a single party.  "The Australian Labor Party" (US spelling) contains a range of factions roughly equivalent to Liberal/National.

12 out of 76 is stable number.  Two territories electing two senators each never produce minor party winners.  The remaining 72, 12 from each of six states, are elected 6 at a time from each state using STV with the Droop quota.  The major parties seem to have a core support base totalling 80-85%.  Consequently, as a general rule, 5 of the 6 seats go to major party candidates and the 6th goes to an independent of minor party candidate.

What is interesting is that the 12 out of 76 members are the reason that any effective democracy occurs between elections in the Australian parliament.  Only in the Senate does the governing party actually negotiate. 

Clearly, a little bit of PR (6 seats per electorate/district) has a big effect.  I don't think the details matter very much.  More PR (eg 20 seats in NSW) doesn't produce significantly different results to the functioning of parliament and government.  Peculiarities, such as Tasmania being relatively over-represented in the federal Senate, don't seem to cause actual adverse effects. 

The lower houses, with their single member seats, are not totally useless and to be done away with.  The vast majority of bills are boring and bipartisan.  They get debated and worked on effectively in the lower house.  There is also the merit of having local representatives who need to satisfy local concerns.

Anthony