Saturday 29 January 2011

AV Voting and the split vote

One of the flaws with FPTP is it's ability to split vote.

So the idea is

Candidate A
Candidate B
Candidate C
and Candidate D

Are all running.

55% of people prefer A over B but some of the would be A voters also vote for C

Candidate A gets 35%
Candidate B gets 40%
Candidate C gets 20%
Candidate D gets 5%

Candidate B wins

So by taking away C we would have got

Candidate A gets 55%
Candidate B gets 40%
Candidate D gets 5%


We will try this example with AV .

Candidate A gets 35%
Candidate B gets 40%
Candidate C gets 20%
Candidate D gets 5%

end result say is
Candidate A gets 55%
Candidate B gets 45%

...

However, say you took out the winning party

Candidate B gets 45%
Candidate C gets 55%


..But what if we take out the runner up instead??

Candidate A gets 35%
Candidate C gets 65%

Perhaps?

...so by taking away the winning OR runner up before the election, we can influence who wins.

It does not end split votes.

8 comments:

  1. OK two things. First of all you're describing voters having an overwhelming change of heart between the first part of your example and the second. If that many really prefer C to A they would have voted C first in the first place and C would have won more initial votes than A in the first round so the case is a nonsense really.

    Secondly in each of your examples of the AV vote, either A or C wins. Clearly A and C are candidates close to each other and favoured by the majority to B and D. However, imagine if the election was done by FPTP instead. Who'd win? B. B would win because of a split vote between similar Candidates A and C and yet B is not as popular as either A or B.

    So your example has really only shown the split vote problems of FPTP, and only by tweaking the situation going against the likely voting patterns of most of the voters have you been able to concoct an idea of AV split votes. Even if it DID work out this way, most people would be happy with either A or C winning compared to B winning.

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  2. Ben...what?
    That is nonsense, I have shown all sides of the argument..

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  3. Just to makes it PERFECTLY clear.
    A i was thinking labour
    B i was thinking tory
    C i was thinking lib dem
    D i was thinking UKIP

    A voters I simulated would vote for A or C
    B voters I Simulated would vote for B,D and then C
    C Voters I simulated would vote for C then A (maybe B afterwards but doesn't affect example anyway if you don't agree)
    D Voters I simulated would vote D then B.

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  4. I probably stretched it that D would go for C after B...SO change that end result to
    A 35% and C 60%

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  5. AV is not a perfect system (maybe there isn't one), but I still see it as head and shoulders over FPTP.

    The scenario you outline for AV above need a very specific set of circumstances to give the outcome you describe - (and can't lead to tactical voting).

    Whereas split votes (and its association with tactical voting) is key to FPTP, and related campaigning. Lib Dems in particular produce endless graphs to show 'we are the only party that can beat [incumbent], forget your principles and everything except "do you want to get rid of [incumbent]"'.

    This particular 'flaw' in FPTP is one of the biggest issues for me - it influences most campaigning, and vote splitting means popular issues (that may attract more than one candidate) are at an immediate disadvantage!

    The risk of splitting also puts parties in control - noone dare run against the official candidate for fear of 'splitting the vote' and 'letting in' an opponent.

    Even if not perfect, a big improvment on FPTP!

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  6. Pop, I needed to force it to go to second preferences and needed atleast 4 candidates, apart from that can use any figures you want.

    Pop, can you see that the AV result can still be changed depending if a potential runner up decides to stand or not?

    This is probably the strongest argument for AV, but lets not deny facts.

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  7. There are (obscure, theoretical) circumstances where there order of elimination can make a difference to the outcome.

    AV isn't perfect, but is still far, far better than FPTP.

    20% of votes have been cited as 'tactical' - all because vote splitting is *essential* to modern politics under FPTP. AV would end that.

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  8. Well I have only read reports that have suggested up to a maximum of 9% but not really the argument to have on this particular post.

    As long as we are in agreement that just like fptp (i am not claiming AV is alone in this), AV result can be changed be changed by splitting the vote.

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