[maemo-community] voting system Re: Final candidate list for Community Council elections

From: Dave Neary dneary at maemo.org
Date: Wed Sep 3 16:29:13 EEST 2008

Frantisek Dufka wrote:
>> I would prefer a single transferable vote system
> How this one works?

You vote in order of preference. Once you get over N/(M+1) votes, where
N votes are cast, and M positions are available.

Allow me an example:

300 voters, electing 2 people from 4 candidates (A, B, C, D).
The quota will then be 300/(2+1) + 1 votes - that is, 101. Once a
candidate reaches 101 votes, they can't be caught by a 3rd place
candidate, and are deemed elected.

A typical vote for an election might be:

A: 1
B: 4
C: 3
D: 2

That is, A is the preferred candidate, D is second, etc.

After the election, we first count how many #1 choices candidates have.
If no candidate is elected at that stage,

A: 107
B:  64
C:  53
D:  76

So, A is elected, and we eliminate C from the election as the candidate
with the fewest votes, and redistribute A's surplus of 6 votes to B and C.

For the 2nd preferences of A, we count how they break down between B, C
and D. Since C is eliminated, if C is a 2nd preference, we look at the
3rd preference. We find that A's 2nd preferences break down 70/30 in
favour of B, and distribute the 6 vote surplus (107 - 101) with 4 votes
going to B, 2 to D:

A: 101 (*)
B: 68
D: 78

We then do the same operation with C's 2nd preferences (and, in the case
where A is 2nd preference, 3rd preferences). This time, there's no
pro-rata calculation, we're simply counting up how many of C's voters
prefer B to D, and vice versa. We find that of C's 53 1st preferences,
26 go to D, 19 go to B, and 8 don't go anywhere (either the person voted
only C as 1st preference, or voted C/A and didn't list a 3rd of 4th

Final result:
A: 101 (*)
B: 68 + 19 = 87
D: 78 + 26 = 104 (*)

where (*) means the candidate is elected.

If we lose so many votes due to untransferrable votes that when we get
down to the last 2 candidates, no-one has passed the quota, the
remaining seat is given to the candidate with the most votes. Imagine,
for example, that only 20 of C's voters voted for D as 2nd preference,
and the extra 6 people didn't give any 2nd preference, we'd have ended
up with

A: 101 (*)
B: 68 + 19 = 87
D: 78 + 20 = 98

And D would be elected, in spite of not having 101 votes.

Hopefully this is clear... it's more complicated to count than it is to
understand from a voter's point of view, but it's been used forever in
Irish elections, and also in Australia, so it has a proven track record.


maemo.org docsmaster
Email: dneary at maemo.org
Jabber: bolsh at jabber.org

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