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Archive for May, 2011

The Maths of AV

There’s been lots of chatter about the ‘complexity’ of AV and that votes get counted more than once. This post will delve into the maths behind AV to prove that votes aren’t counted more than once. Plus, ranking things in order of preference is pretty simple.

Let’s assume that there are four candidates and the voter uses three preferences 1, 2, and 3.

1=x 2=y 3=z

Assume that the vote goes through three rounds.

First Round

x=x

1x=x

1=1

Second Round

x=y-x

2x=y

2=1

Third Round

x=z-y

3x=z

3=1

Now to explain the maths.

Why does x=y-x or x=z-y?

Because the current preference must have the previous preference subtracted from it.  If we replace the letters with numbers it equates to 1=2-1 and 1=3-2.

Why is there a multipler, such as 2x?

Because it is used to indicate which round of voting the vote is currently in.

Therefore, at the end of the three rounds, the third preference still has the same value as the initial vote cast, it’s not worth more or less, it’s just a redistribution.

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