It is important to understand that a bunch of clever people have thought hard about voting systems; we don’t have to invent this. I remember that our management in Sun Professional Services tried to imbue us with the mantra, “Innovate, Don’t Reinvent” and others have declared that the process of innovation is standing on the shoulders of giants. Voting system qualities known as criteria have been defined. There may be some as yet undiscovered criteria, but it would be best if we debate the pro’s and con’s using an agreed categorisation and science.

One has to be brilliant to be both in a minority and right, and most of us are not that brilliant.

Wikipedia, on their article, Comparison of Electoral Systems, says this,

Attitudes towards systems are highly influenced by the systems’ impact on groups that one supports or opposes, which can make the objective comparison of electoral systems difficult. … To compare methods fairly and independently of political ideologies, voting theorists use voting method criteria, which define potentially desirable properties of voting methods mathematically.

Wikipedia – Comparison of Electoral Systems

One thing we should note is that not all criteria can be applied to all systems, the key differences are between single winner systems, and multiple winner systems and then between list based and non-list based systems.

While some consider and seek to judge instant run off elections, sometimes referred to as the Alternate Vote as a special case of STV i.e. an STV with only one winner, the fact that there is only one winner makes it a separate and quite different system. This is shown by the fact that it passes and fails different voting criteria. Also, in AV elections, there is no transfer of a surplus votes and the minority i.e. the wasted voted can be as high as 50% – 1. This is better than simple plurality systems where the losing proportion can easily be quite high majorities. It seems to me that one critical goal of democratic voting systems should be to ensure that the “wasted” or losing votes are as small as possible.

Some criteria only apply to singe winner elections, and while it’s hard to game an STV election, it is not impossible. Games can be played by candidate/parties or by voters. STV’s problems come from the fact that surpluses and eliminations occur in an order and thus transfers are impacted by this ordering.

The Wikipedia article tests STV against 7 voting systems criteria and fails it on five. Some of the criteria seem to be remarkably similar and, it seems to me, all relate to honesty and motivation in voting behaviour and how the voting system reflects this honesty. STV fails the Monotonicity Criterion as there are cases where you can support your preferred candidate by down ranking them. It fails the Consistency criterion, probably by design and I am not sure it’s all that desirable, but this is about sub-set aggregation which can’t be done in STV. It also fails the Participation criterioan, that your voice is always stronger if you vote, and “No favourite betrayal”, where you have no incentive to vote for anyone other than your favourite.

It’s certainly not perfect but we should learn from thinkers that have gone before us.

Voting Systems Theory and STV
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2 thoughts on “Voting Systems Theory and STV

  • 7th July 2020 at 7:53 pm
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    Much of the debate in the UK has focused on Parliament which would in my mind benefit from some form of proportional representation. This has been championed by the LD using STV as their flagship scheme, which is designed to be anti-party and the LibDem hope is that votes will ‘bleed’ to them from both the Tories and Labour although that hope is probably out-dated by both the coalition and the Tory 2019 victory. However, when it comes to PR, in the UK we have often chosen systems based on Party Lists which is an alternative to STV. This is an important dichotomy in reviewing PR systems,

  • 9th July 2020 at 9:43 am
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    I wrote another piece on the problems for Party Managers but further reading means I want to highlight the Gibbard–Satterthwaite theorem which states, according to wikipedia, that voting systems, with more than two outcomes will always enable tactical voting. This built on Arrow’s impossibility theorem which makes similar claims but restricts the proposition to ranked voting systems.

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