NAME

Vote::Count::IRV

VERSION 1.00

IRV

Implements Instant Runoff Voting for Vote::Count.

SYNOPSIS

  use Vote::Count::Method;
  use Vote::Count::ReadBallots 'read_ballots';

  my $Election = Vote::Count::->new(
    BallotSet => read_ballots('%path_to_my_ballots'), );

  my $result = $Election->RunIRV();
  my $winner = $result->{'winner'};

  say $Election->logv(); # Print the full Log.

Method Summary

Instant Runoff Voting Looks for a Majority Winner. If one isn't present the choice with the lowest Top Count is removed.

Instant Runoff Voting is easy to count by hand and meets the Later Harm and Condorcet Loser Criteria. It, unfortunately, fails a large number of consistency criteria; the order of candidate dropping matters and small changes to the votes of non-winning choices that result in changes to the dropping order can change the outcome.

Instant Runoff Voting is also known as Alternative Vote and as the Hare Method.

Tie Handling

There is no standard accepted method for IRV tie resolution, Eliminate All is a common one and the default.

Returns a tie when all of the remaining choices are in a tie. An optional value to RunIRV is to specify tiebreaker, see TieBreaker.

RunIRV

  $Election->RunIRV();

  $Election->RunIRV( $active )

  $Election->RunIRV( $active, 'approval' )

Runs IRV on the provided Ballot Set. Takes an optional parameter of $active which is a hashref for which the keys are the currently active choices.

Returns results in a hashref which will be the results of Vote::Count::TopCount->EvaluateTopCountMajority, if there is no winner hash will instead be:

  tie => [true or false],
  tied => [ array of tied choices ],
  winner => a false value

Supports the Vote::Count logt, logv, and logd methods for providing details of the method.

TieBreaker

Uses TieBreaker from the TieBreaker Role. The default is 'all', which is to not break ties. 'none' the default for the Matrix (Condorcet) Object should not be used for IRV.

All was chosen as the module default because it is Later Harm safe. Modified Grand Junction is the most resolveable and is the recommended option.

In the event that the tie-breaker returns a tie eliminate all that remain tied is used, unless that would eliminate all choices, in which case the election returns a tie.

BUG TRACKER

https://github.com/brainbuz/Vote-Count/issues

AUTHOR

John Karr (BRAINBUZ) brainbuz@cpan.org

CONTRIBUTORS

Copyright 2019 by John Karr (BRAINBUZ) brainbuz@cpan.org.

LICENSE

This module is released under the GNU Public License Version 3. See license file for details. For more information on this license visit http://fsf.org.