Tuesday, 3 May 2011

Alternative Vote: a question

On the 5th of May there will be a national referendum on whether we should switch to the Alternative Vote system, also known as the Instant Run-off system. In AV voters rank candidates in preference order and in each round of counting the candidate with the lowest pile of votes drops out and their pile is re-allocated to the other candidates.

Here's a quiz.

In the first round of counting the following results are seen:

Candidate A: 100 first preference votes
Candidate B: 99 first preference votes
Candidate C: 99 first preference votes

Question: what happens next?


chefdave said...

B & C are eliminated and A is declared the winner? Who knows?

I've come up with a few scenarios like this to point out the flaws in AV but advocates aren't having any of it!

One of it's main drawbacks is the inconsistency, under normal conditions the last placed candidate is eliminated and his 2nd preference is then treated as being on par with others' first choice, thus giving an absolute majority.

But what happens if 100 voters all vote Lab 1st, Lib 2nd and Con 3rd? In this instance 2nd and 3rd votes are viewed as worthless, despite the candidate polling an equal number of votes.


labour get 50% of 1st preference votes Libs 25% and Con 25% but they all put BNP as their 2nd preference.

It's full of holes.

Nationalist said...

Indeed, you would have thought there would be some way of looking at second preferences, but the system doesn't seem to provide it.

Anonymous said...

It's easy we do exactly what happens in an English election now when there is a draw for first place, have a few recounts and if it is still even the returning officer tosses-a-coin or something (between B and C) then the loser is eliminated and we are left with A and B and on we go... Why do you see anything wrong with this?