PR in Cambridge Mass -- a case of city-level STV
- Tom Monto
- Feb 28, 2024
- 3 min read
Updated: Mar 18
Cambridge (Mass.) city elections
Nine councillors elected, in November in odd-numbered years.
later, councillors elect the mayor from among their own group.
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2023 Cambridge Mass election
nine seats to fill
24 candidates
quota 2334
top 9 in first count
all elected at the end
Sumbul Siddiqui | +3353 | 3353 | ELECTED -- 1st count |
Burhan Azeem | +2250 | 2250 | CONTINUING |
Patricia M. Nolan | +2156 | 2156 | CONTINUING |
Marc C. McGovern | +2064 | 2064 | CONTINUING |
Paul F. Toner | +1987 | 1987 | CONTINUING |
Jivan G. Sobrinho-Whee. | +1486 | 1486 | CONTINUING |
E. Denise Simmons | +1450 | 1450 | CONTINUING |
Ayesha M. Wilson | +1168 | 1168 | CONTINUING |
Joan F. Pickett | +932 | 932 | CONTINUING |
"Final"
(As I tell below, these vote tallies are partly based on un-necessary final vote transfers)
Sumbul Siddiqui | 0 | 2334 | ELECTED -- 1st count |
Burhan Azeem | 0 | 2334 | ELECTED -- 2nd count |
Marc C. McGovern | 0 | 2334 | ELECTED -- 8th count |
Patricia M. Nolan | 0 | 2334 | ELECTED -- 8th count |
Paul F. Toner | 0 | 2334 | ELECTED -- 11th count |
Jivan G. Sobrinho-Whee. | 0 | 2334 | ELECTED -- 15th count |
E. Denise Simmons | 0 | 2334 | ELECTED -- 16th count |
Ayesha M. Wilson | +113 | 2334 | ELECTED -- 17th count |
Joan F. Pickett | +107 | 2248 | ELECTED -- 17th count |
all nine were in winning position in the first count. (no lower-ranking candidate "turnover")
if vote count process (the transfers) had ended immediately following Count 16 when there was only one more candidate than the number of remaining open seats,
then this would have been the final vote tallies:
Sumbul Siddiqui | 0 | 2334 | ELECTED 1st Count |
Burhan Azeem | 0 | 2334 | ELECTED -- 2nd count |
Marc C. McGovern | 0 | 2334 | ELECTED -- 8th count |
Patricia M. Nolan | 0 | 2334 | ELECTED -- 8th count |
Paul F. Toner | 0 | 2334 | ELECTED -- 11th count |
Jivan G. Sobrinho-Whee. | 0 | 2334 | ELECTED -- 15th count |
E. Denise Simmons | +90 | 2334 | ELECTED -- 16th count |
Ayesha M. Wilson | +259 | 2221 | CONTINUING (set to be elected) |
Joan F. Pickett | +483 | 2141 | CONTINUING (set to be elected) |
Ayah A. Al-Zubi | +72 | 1525 | [set to be defeated next] |
Al-Zuba was declared defeated after this count.
Wilson and Pickett elected with partial quota. only 100 and 200 less than quota respectively
Al-Zubi neither elected nor eliminated 1525 votes*
exhausted votes 1114 votes
total wasted 2639 votes
*Al-Zubi's votes were transferred in (un-necessary) "Final Count" and only about 200 of his supporters had marked either Wilson or Pickett as one of the preferences (anywhere at all on their ballot) so almost all of Al-Zubi's votes went to exhausted pile, but seats were filled anyway by that time.
in un-necessary "final Count"
one elected with partial quota.
Wilson won with exactly quota
of 23,339 valid votes
8 times quota 18,672
20,920 effective votes
approx. nine times quota 10X Q = 23,339 - 2334 = 21,005
1305 exhausted
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Cambridge STV vote transfer tables online:
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more analysis
2023 Cambridge
23,339 valid ballots.
Electing 9 candidates.
Quota is 2334 votes. (1/10th of valid votes , plus 1)
There were 173 invalid ballots.
20,920 votes used to elect the winners.
16,846 were cast in first round for a winner,
so never transferred except maybe as a surplus vote.
Cambridge election method statement says every nth votes used for surplus votes. so apparently they use "non-random random" (Chicago style, I think it was called)
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An un-quantifiable measure of fairness is presented by the fact that under STV a voter may see his or her first choice elected but the vote not being used for that purpose. And a voter may see all of their first three preferences elected but again with their own vote not being used for that result.
One instance where that was calculated was in an analysis of the
Cambridge (Massachusetts) city election of 2021:
- 90 percent of voters saw their vote help to elect a candidate;
- more than 65 percent of voters saw their first choice candidate elected, and
- more than 95 percent of voters saw at least one of their top three choices elected. (Wiki: STV).
Note that 95 percent of the votes were not used to elect the winners, but one or more of the voter's marked candidate-specific preferences were elected in 95 percent of the cases (even if vote itself was not used to elect anyone).
So a high rate of satisfied voters.
It seems list PR secures about the same rate of effective votes as STV (sometimes less, sometimes more), but all the votes used effectively under list PR are first preference by party - with the voters having very little discretion as to which individual candidate the votes goes (the first listed candidates on the party list are the most likely to be elected).
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