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PR in Cambridge Mass -- a case of city-level STV

Tom Monto

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

2334 

 ELECTED -- 1st count

Burhan Azeem

2334 

 ELECTED -- 2nd count

Marc C. McGovern

2334 

 ELECTED -- 8th count

Patricia M. Nolan

2334 

 ELECTED -- 8th count

Paul F. Toner

2334 

 ELECTED -- 11th count

Jivan G. Sobrinho-Whee.

2334 

 ELECTED -- 15th count

E. Denise Simmons

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

2334 

ELECTED 1st Count

Burhan Azeem

2334 

 ELECTED -- 2nd count

Marc C. McGovern

2334 

 ELECTED -- 8th count

Patricia M. Nolan

2334 

 ELECTED -- 8th count

Paul F. Toner

2334 

 ELECTED -- 11th count

Jivan G. Sobrinho-Whee.

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:

=============================================

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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History | Tom Monto Montopedia is a blog about the history, present, and future of Edmonton, Alberta. Run by Tom Monto, Edmonton historian. Fruits of my research, not complete enough to be included in a book, and other works.

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