The single transferable vote — STV — is a proportional system that 22 American cities tried between 1915 and the 1950s. Of those, only Cambridge, Massachusetts, still uses STV.
STV relies on preferential ballots, but ballots are counted very differently than with other preferential systems. With STV, votes for the most popular candidates are transferred to less popular ones.
To see how that works, consider an example. To start, the number of votes needed to win an STV seat = 1+ (Number of votes cast)/(Number of seats to be filled + 1)
So, if 240,000 citizens vote for a seven-member council, winning a seat takes 1+ 240,000/8 = 30,001 votes.
Suppose, then, that the most popular candidate draws 50,001 first-choice votes. In that case, 20,000 are considered “excess” and go to his voters’ second choices. That is, each voter for the most popular candidate has 40 percent of their vote go to their second choice. Then, if any candidate reaches 30,001 votes, she wins a seat, and her excess votes go to her voters’ next choices.
What if no one gets 30,001 votes? Then, the lowest-drawing candidates are dropped one by one, and their votes go to the next candidates on those ballots until some candidate exceeds 30,001 votes. Then his excess votes are transferred to the next candidates on those ballots, and so on.
Unsurprisingly, STV strikes many people as tough to understand, even arbitrary.
STV also undercuts the link between each representative and his/her constituents. For instance, in the above case, 50,001 people who want to be represented by person A are required to give 40 percent of their votes — in effect 40 percent of their clout — to other representatives. Who, then, represents each voter? Who is each representative accountable to? With STV, it’s ambiguous.
That may help explain why, of the 22 U.S. cities that tried STV, 21 ended up repealing it.
Some advocates for STV claim that those cities repealed it because many voters objected to minorities winning more representation than in the past, because the Republican and Democratic parties objected to losing their legislative monopoly, and because before computers, it took weeks to count STV ballots and determine who won.
But these explanations ignore a critical question, which is: Did most people living under STV believe that it had improved the quality of their city government? In fact, many voters felt that STV had reduced the quality of government. In Toledo, for instance, the local newspaper blamed STV for “lax administration.” (See Proportional Representation and Electoral Reform in Ohio, Ohio State University Press, 1995, edited by Kathleen Barber.)
STV does, however, seem to work in Ireland. But Ireland is parliamentary. That is, Parliament’s main role is to pick the prime minister who picks the cabinet and sets national policy. STV is in effect a reasonable way to determine which party or parties choose the head of government.
But STV does not link lawmakers and voters in a way that promotes constructive negotiation.