Majority judgment

Majority Judgment is a single-winner voting system proposed by Michel Balinski and Rida Laraki. Voters freely grade each candidate in one of several named ranks, for instance from "excellent" to "bad", and the candidate with the highest median grade is the winner. If more than one candidate has the same median grade, a tiebreaker is used which sees how "broad" that median grade is. It can be considered as a form of Bucklin voting which allows equal ranks.

Voting process

Voters are allowed rated ballots, on which they may assign a grade or judgment to each candidate. Badinski and Laraki suggest six grading levels, from "Excellent" to "Reject". Multiple candidates may be given the same grade if the voter desires.

The median grade for each candidate is found, for instance by sorting their list of grades and finding the middle one. If the middle falls between two different grades, the lower of the two is used.

The candidate with the highest median grade wins. If several candidates share the highest median grade, all other candidates are eliminated. Then, one copy of that grade is removed from each remaining candidate's list of grades, and the new median is found, until there is an unambiguous winner. For instance, if candidate X's sorted ratings were {"Good", "Good", "Fair", "Poor"}, while candidate Y had {"Excellent", "Fair", "Fair", "Fair"}, the rounded medians would both be "Fair". After removing one "Fair" from each list, the new lists are, respectively, {"Good", "Good", "Poor"} and {"Excellent", "Fair", "Fair"}, so X would win with a recalculated median of "Good".

Satisfied and failed criteria

Majority Judgment voting satisfies the majority criterion for rated ballots, the mutual majority criterion, the monotonicity criterion, reversal symmetry, and later-no-help. Assuming that ratings are given independently of other candidates, it satisfies the independence of clones criterion and the independence of irrelevant alternatives criterion - although this latter criterion is incompatible with the majority criterion if voters shift their judgments in order to express their preferences between the available candidates.

It fails the Condorcet criterion, later-no-harm, consistency, the Condorcet loser criterion, and the participation criterion. It also fails the ranked or preferential majority criterion, which is incompatible with the passed criterion independence of irrelevant alternatives.

Example application

Suppose that Tennessee is holding an election on the location of its capital. The population is concentrated around four major cities. All voters want the capital to be as close to them as possible. The options are:

• Memphis, the largest city, but far from the others (42% of voters)
• Nashville, near the center of the state (26% of voters)
• Chattanooga, somewhat east (15% of voters)
• Knoxville, far to the northeast (17% of voters)

The preferences of each region's voters are:

42% of voters Far-West	26% of voters Center	15% of voters Center-East	17% of voters Far-East
Memphis Nashville Chattanooga Knoxville	Nashville Chattanooga Knoxville Memphis	Chattanooga Knoxville Nashville Memphis	Knoxville Chattanooga Nashville Memphis

If there were four ratings named "Excellent", "Good", "Fair", and "Poor", and each voter assigned four different ratings to the four cities, then the sorted scores would be as follows:

City	↓ Median point
Nashville
Chattanooga
Knoxville
Memphis
	Exellent      Good      Fair      Poor

The median rating for Nashville and Chatanooga is "Good"; for Knoxville, "Fair"; and for Memphis, "Poor". Nashville and Chatanooga are tied, so "Good" ratings have to be removed from both. After removing 16% "Good" ratings from the votes of each (where 16% is the minimum number that attains different medians for the two cities), the sorted scores become:

City	↓ Median point
Nashville
Chattanooga
	Removed ratings (sorted to both ends evenly for easy comparison of medians with above).

Chatanooga's now has the same number of "Fair" ratings as "Good" and "Excellent" combined, so its median is rounded down to "Fair", while Nashville's remains at "Good" and so Nashville, the capital in real life, wins.

If voters from Knoxville and Chattanooga were to rate Nashville as "Poor" and/or both sets of voters were to rate Chattanooga as "Excellent", in an attempt to make Chatanooga win, which would be a better outcome for them, the winner would still be Nashville.

History

This system has several salient features, none of which is original in itself. It is a rated system. Since such systems include approval voting, which has been independently reinvented many times, this aspect is probably the least original. However, voting theory has tended to focus more on ranked systems, so this still distinguishes it from most voting system proposals. It uses words, not numbers, to assign a commonly-understood meaning to each rating. Again, this aspect is unusual but not unheard-of throughout the history of voting. Finally, it uses the median to aggregate ratings. This method was explicitly proposed to assign budgets by Francis Galton in 1907 and was implicitly used in Bucklin voting, a system used soon thereafter in Progressive era reforms in the United States.

The full system of Majority Judgment was first proposed by Badinski and Laraki in 2007. That same year, they used it in an exit poll of French voters in the presidential election in the Bayrou area. Although this regional poll was not intended to be representative of the national result, it agreed with other local or national experiments in showing that Bayrou, rather than the eventual runoff winner Sarkozy, would have won under most alternative rules, including Majority Judgment. They also note that:

Everyone with some knowledge of French politics who was shown the results with the names of Sarkozy, Royal, Bayrou and Le Pen hidden invariably identified them: the grades contain meaningful information.

It has since been used in judging wine competitions and in other political research polling in France and the US.

See also

• List of democracy and elections-related topics
• Voting system

References

• Balinski, Michel, and Laraki, Rida (2010). Majority Judgment: Measuring, Ranking, and Electing, MIT Press