Methods of Decision-Making

Typology

Peter Emerson on The METHODS OF DECISION-MAKING:

Binary (Two-option) Methodologies

i) Majority voting, which may be subject to a simple (50% + 1), weighted (2/3rds or some other fraction greater than ½), double (sometimes used in Switzerland, when success depends upon a majority of the voters and a majority of the cantons), qualified (as in the European Union, so bigger countries have more clout), or consociational (as in Belgium or Cyprus, where the parliamentarians or electorate are divided into two constituencies and in which success depends on both majorities; in Bosnia in 1990, a three-way version was attempted… in vain).

Multi-option Non-Preferential Methodologies

ii) Plurality voting, in which voters cast only a 1st preference, and the option with the highest number of 1st preferences wins.

iii) The two-round system TRS, is a plurality vote is followed by a majority vote if no one option wins a majority in the first round.

iv) In approval voting, the voter may ‘approve’ of more than one option, but each ‘approval’ has the same value – there are no preferences – and the option with the most ‘approvals’ wins. Range voting gives the voter a fixed number of points that he/she can distribute to the various options at will: either some points to each of two or more options, or all the points to just one option and none to any of the others.

v) Serial voting, in which, say, proposed amendments are listed in order, (cheap to expensive, or whatever); the procedure is a series of majority votes between the two extreme options, with the loser being eliminated after each vote; the outcome is a Condorcet winner (but see below). Multi-option Preferential Methodologies

vi) The alternative vote AV, (also known as instant run-off voting IRV, preference voting PV, and the single transferable vote STV), [5] allows the voter to cast preferences for one, some or all the options listed. The count is a series of multi-option votes, the least popular being eliminated after each stage and its votes transferred in accordance with its voters’ 2nd and next highest preferences, until one option gains majority support.

vii) A Borda count BC, asks the voters to cast their preferences, and points are awarded to (1st, 2nd … last) preferences cast according to the rule (n, n-1 … 1) or (n-1, n-2 … 0); this procedure may encourage the voters to truncate their vote. A Modified Borda Count MBC, allows for partial voting. It uses M de Borda’s original formula: [6] (m, m-1 … 1), and this encourages the voters to cast a preference for every option.

viii) The Condorcet rule in which the preferences cast for each option are compared with those of every other option, in turn. The option which wins the most pairings and therefore beats every other option – if there is one – is the Condorcet winner. If there isn’t one, the option which wins the most pairings is chosen, (the Copeland rule). There may, however, be a paradox.

The MBC and Condorcet are the only methodologies which always take all preferences cast by all voters into account; not least for this reason, they can be claimed to be the most inclusive and therefore most consensual procedures, and provide the most accurate measure of the will of the said set of voters. Indeed, in many voters’ profiles, the MBC social choice is also the same as the Condorcet social choice. What’s more, experience suggests that on many occasions, the MBC social choice is the same as the Condorcet social choice, and even the social rankings are often similar."