IN PRACTICE: CAMBRIDGE, MA
Our Types of RCV page provides a basic understanding of how to elect multiple candidates using proportional ranked choice voting. However, the counting procedure is a little more complicated and varies somewhat by jurisdiction. This page provides an in-depth explanation of how Cambridge, Massachusetts, tabulates proportional RCV elections.
In 1939, the City of Cambridge adopted a city charter electing nine City Councilors and six School Committee members at-large using proportional RCV. With Cambridge's system, a candidate must win a certain proportion of the votes to be elected. This winning fraction of the votes is known as the threshold, or "quota," to win the election.
DETERMINING THE THRESHOLD
The threshold is determined by dividing the total number of valid ballots cast by the number of positions to be elected plus one and then adding one to the resulting dividend.
Thus, to elect nine City Councilors, the total number of valid ballots cast is divided by ten. To elect six School Committee members, the total number of valid ballots cast is divided by seven. And in both cases, one is added to the result of the division.
For example, if 25,000 valid ballots are cast for City Council, the threshold will be 2,501 (25,000 divided by 10, plus 1).
COUNTING THE BALLOTS
The count begins by sorting ballots by the first choice, or Number 1 choice, selected on each valid ballot. This process is generally known as the "First Count."
Any candidates who reach the threshold with first choices are declared elected. Any extra votes they receive beyond the threshold transfer to the next ranked candidates on those ballots. These extra votes are known as surplus votes. For more information on surplus votes, see Transferring the Surplus on Cambridge’s website.
The count continues by eliminating any candidates that received fewer than fifty votes in the first count. Those ballots then transfer to the next ranked candidate on each ballot.
[To understand how to mark RCV ballots, see How RCV Works.]
If no candidate crosses the election threshold after all ballots transfer, the candidate with the lowest number of votes is eliminated. Their ballots then transfer to the next ranked choice on each ballot.
Candidate vote totals continue to grow as ballots transfer from eliminated candidates. As candidates reach the threshold through rounds of elimination and ballot transfer, they are declared elected. No additional ballots transfer to them.
This process continues until all candidates have been eliminated except the nine winners for City Council or the six winners for School Committee.
TRANSFERRING THE SURPLUS
The technique used by Cambridge for selecting ballots to transfer from a candidate's surplus to bring the candidate down to the threshold is called the Cincinnati Method. The method proceeds in two steps:
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First, every ballot counting for a candidate with surplus votes is numbered sequentially based on the order in which it was counted.
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Second, every nth ballot is drawn and transferred to a continuing candidate. Surplus ballots transfer until the original candidate has a number of ballots equal to the threshold. "n" is the nearest whole number computed by the formula:
