# [EM] IRV proponents figure out how to make IRV precinct-summable

Dave Ketchum davek at clarityconnect.com
Tue Mar 24 18:21:03 PDT 2009

```Ouch - What I said about IRV missed a bit.  Matters little for I still
dislike IRV or Contingent Vote (which I read as running a bit faster
and more often picking the wrong winner).

On Mar 24, 2009, at 10:28 AM, Raph Frank wrote:

> On Tue, Mar 24, 2009 at 2:30 AM, Dave Ketchum <davek at clarityconnect.com
> > wrote:
>> Let's try it slowly for IRV, assuming multiple districts to avoid
>> shortcut
>> temptations:
>>
>> 1  Count ala Plurality.  If leader has a majority, that is winner.
>>
>> 2 Sum vote counts, starting with weakest count and ending before
>> doing the
>> next candidate that would make a majority.  None of those counted
>> could win,
>> so mark them all as losers and go back to step 1.
>
> That isn't true.
>
> The rule is actually that you can eliminate the weakest N candidates
> in one step, if the sum of their votes is less than the (N+1)th
> weakest candidates.  The procedure is then to find the largest
> possible N.
>
> 40: A
> 25: B
> 15: C>E>B
> 9: D>E>B
> 7: E>B
> 4: F>E>B
>
> Round 1:
> A: 40
> B: 25
> C: 15
> D: 9
> E: 7
> F: 4
>
> According to your rules, eliminate F+E+D+C.  Eliminating B as well
> would cause a majority of votes, so B is safe.
>
> Round 2:
> A: 40
> B: 60
>
> B wins
>
> However, with full IRV, the results are
>
> eliminat F
>
> Round 2
> A: 40
> B: 25
> C: 15
> D: 9
> E: 7+4 = 11
> F: -
>
> Eliminate D
>
> Round 3
> A: 40
> B: 25
> C: 15
> D: -
> E: 9+11 = 20
> F: -
>
> Eliminate C
>
> Round 3
> A: 40
> B: 25
> C: -
> D: -
> E: 20+15 = 35
> F: -
>
> Eliminate B
>
OOPS here - The B voters did not name a next rank so 40 A beats 35 E!

DWK

> Round 4
>
> A: 40
> B: -
> C: -
> D: -
> E: 35+25 = 60
> F: -
>
> E wins
>
> So, the result is different.
>
>>> Less formally, the method is summable if you can "count in
>>> precincts" to
>>> produce managable data chunks that can then be combined to get the
>>> result
>>> for all precincts or districts involved, no matter the size of each
>>> district.
>>>
>> Not clear how this helps.  You have to get the totals for round 1
>> to decide
>> how to proceed - matters not how many chunks.
>
> I guess IRV is "summable in precincts, subject to central office
> instructions".
>
> An election can be verified by checking all the precinct sums/counts
> and that the central instructions were correct, assuming that the
> precinct sums were also correct.

```