Supplementary Voting

Supplementary Voting is a short-cutted STV system.

Majority support is required to win.

Voters mark first preference and one back-up preference.

Votes are counted.

If no candidate receives majority in the first count, all but the two most popular candidates are eliminated, and reference is made to the backup preferences marked on those ballots. With only two surviving, one or the other will necessarily have a majority when votes are then counted.

Like runoff elections, majority is assured.

Like Alternative Voting (Instant Runoff Voting), SV has

- single-seat districts.

- ranked ballots.

But unlike AV, SV

- does not allow votes to rank more than two candidates.

- does not allow voters themselves to choose a winner other than the two most popular in the First Count. (Although in AV, it is seldom or never that the third most-popular in the initial count is elected in the end.)

In SV, say with five candidates in the running, a voter who backs one of the lesser candidates in the first count has a blind chance of two in four ( of putting his or her back-up preference on someone who will survive to the next round, where a candidate has a 50-50 chance of being elected.

If voter could have an idea during the process who is being dropped off, then he or she could plan better where to put back-up preferences.

But in Alternative Voting, like sending someone off on a shopping trip

- raspberry yogurt if you find it, if not, then blueberry, if not then lemon --

the voter can mark back-up preferences to say if this candidate is dropped, I would like that one -- if that one dropped, I would like the other, etc.

With only two marked preferences, there is not much flexibility - not much redundancy - and there is consequently much waste of votes.

The Alternative Voting system used in London (Ontario) city election in 2018 is hardly more than Supplementary Voting as voters could only mark three preferences.

However at least in that, the field was not immediately lowered to only two. The field was gradually one by one reduced until a person had the support for more than half the voters, through a combination of first preferences and transfers from other candidates.

Unlike Supplementary Voting (SV), STV uses

- multi-member districts or at-large districts

- allows votes to rank more than two candidates.

- allows voters themselves to choose a winner other than the two most popular in the First Count.

And most importantly unlike STV, SV does not produce proportionality, through mixed representation.

But SV does ensure that the successful candidate has the support of the majority of the voters.

For that reason it is unfortunate that now in Britain the election of mayor of London is to switch from SV to FPTP, where majority support is not required at all.

Thanks for reading.

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