Floor Rules

In real elections it is common to have choices with very little support, the right to write-in and the obligation to count write-ins can produce a large number of these choices, with iterative dropping like IRV it can take many rounds which have to be logged into the election report to work through them. A Floor Rule sets a criteria to remove the weakly supported choices early in a single operation. If you are implementing a Hand-Count compatible process having an aggressive Floor Rule can be a benefit.


  my $Election = Vote::Count->new( BallotSet => $someballotset );
  my $ChoicesAfterFloor = $Election->ApprovalFloor();
  $Election->Active( $ChoicesAfterFloor ); # To apply the floor

The Floor Methods

All Methods in this Module apply a floor rule, log the eliminations and return the set of remaining choices as an Active Set. They do not set the Election's active set, since it is possible that this isn't the desired action.

ApprovalFloor, TopCountFloor

Requires a percent of votes cast in Approval or TopCount. The default is 5% for Approval and 2% for TopCount.

  # TopCountFloor with 3% threshold.
  my $Floored = $Election->TopCountFloor( 3 );

Both of these methods take an optional parameter which is the percentage for the floor. If the parameter is 1 or greater the parameter will be interpreted as a percentage, if it is less than 1 it will be interpreted as a decimal fraction, .1 and 10 will both result in a 10% floor.

For Range Ballots using ApprovalFloor there is an additional optional value for cutoff that sets the score below which choices are not considered approved of.

  # Applies 5% floor with cutoff 5 (appropriate for Range 0-10)
  my $active = $Range->ApprovalFloor( 5, 5 );

TCA (TopCount-Approval)

Aggressive but (effectively) safe for Condorcet Methods. It requires the Approval for a choice be at least half of the leading Top Count Vote.

This rule takes no optional arguments.

TCA Rule Validation and Implication

If there is a Loop or Condorcet Winner, either it will be/include the Top Count Leader or it must be a choice which defeats the Top Count leader. To defeat the Top Count Leader a Choice's Approval must be greater than the Lead Top Count. To be able to defeat a choice it is necessary to have more than half of the approval of that choice. Thus to be able to defeat a choice which can defeat the Top Count Leader it will be necessary to have more than half of the Approval of a choice with an Approval greater than the lead Top Count.

There is a small possibility for a situation with a deeply nested knotted result that this rule could eliminate a member of the Dominant Set. For the common simple dropping rules (Approval, Top Count, Greatest Loss, Borda) this choice would never win.

For IRV any choice with an Approval that is not greater than the current TopCount of any other choice will always be eliminated prior to that choice. Unfortunately, with IRV any change to dropping order can alter the result. If it is used in IRV the Election Rules must specify it. Also because it is a high Approval based Floor, it can be construed as adding a small risk of Later Harm violation. If the reason for choosing IRV was Later Harm, then the only safe floor is a TopCount floor.



John Karr (BRAINBUZ)


Copyright 2019 by John Karr (BRAINBUZ)


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