STV in an issue space
by Kevin Venzke [Home]

This page illustrates the results of STV using a two-dimensional issue space. By reducing the winner count to one, IRV can also be demonstrated. There are always 10 candidates, but the number of preferences expressed by the voters can be adjusted, to view the effects of missing out on some of the preference information. By reducing the preferences to just one, with two STV winners (noting that no preferences would be able to transfer), you can simulate an ordinary two-round runoff.

The original concept: Three-winner STV in a two-round single-winner method

The original intent of this page was to explore the possibility of using three-winner STV as the first phase of a two-round single-winner method. Suppose that three candidates are found who represent the voters evenly. If voters were obliged to rank all three candidates, we would have a good chance of finding the median voter's preferred candidate, either because there is a majority favorite (perhaps if the three candidates were not chosen well) or because, assuming voter sincerity and the validity of the notion of an underlying issue space, the median voter's first preference might receive no or nearly no last preferences. (Though for strategy reasons we probably wouldn't actually use "minimum last preference count" as an election method.)

The likely truth of this is more obvious if the "plot height" of the issue space is small, since it's harder then to divide the electorate into thirds without a clear center.

Some details on the plots
Each dot represents one vote plus a small random amount. Candidates are also voters. In the second plot, voters are colored according to some candidate that they helped to elect with at least 1/4th of their vote. When there are multiple such candidates for the voter, one is chosen at random to provide the color. Voters who are unable to contribute to the election of any candidate remain colored black.

    Number of voters: 
    Plot height: 

    Distribution options:     even    pull half    push half    triangle
Dynamic adjustments
    Voters rank top X preferences: 
    How many STV winners: 
  (use - = [ ] to adjust these values)

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