The single transferable vote — STV — is the proportional election system that 22 American cities tried between 1915 and the 1950s. With STV, as in other proportional systems, a typical voter is likely to get at least one representative who shares the voter’s political orientation, far more likely than with America’s current majoritarian system. Even so, of the original 22 cities that tried STV, only one still uses it: Cambridge, Massachusetts.
To understand why, we first need to look at how it works: STV relies on preferential ballots, in which voters rank the candidates they prefer in order. 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 the implications, 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 his/her vote go to his second choice. If any candidate thereby reaches 30,001 votes, she wins a seat. Her excess votes then 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. His excess votes are then transferred to the next candidates on those ballots, and so on.
Why did most voters eventually reject this method? The answer depends on whom you ask. STV advocates usually give three explanations: 1) Many voters objected to minorities winning more representation than in the past. 2) It took weeks to count STV ballots and determine who won (this was in the days before computers). 3) The Republican and Democratic parties lost their legislative monopoly and therefore campaigned relentlessly against STV.
But these explanations leave out three crucial points:
1) STV's mechanics are difficult for the average voter to understand.
2) STV undercuts the link between each representative and his/her constituents. For instance, in the example above, 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? With STV, it’s ambiguous.
Who is each representative accountable to? With STV, it’s ambiguous.
3) Most voters who lived under STV felt that it reduced the quality of government. In Cleveland, for instance, voters were “disillusioned by [STV’s] failure to prevent partisan deals, patronage, bribery and graft.” In Cincinnati, “partisanship and dissatisfaction with governance . . . contributed to [STV’s] repeal.” And in Toledo, the local newspaper blamed STV for “lax administration.” (See Barber, Kathleen, ed., Proportional Representation and Electoral Reform in Ohio. Ohio State University Press, 1995, pp 130, 173, 253.)
Nonetheless, STV has seemed to work in Ireland for most of the past century. But Ireland is parliamentary. That is, Parliament’s main role is to pick the prime minister who picks the cabinet, which jointly set national policy. Voters therefore tend to hold the prime minister — and the parties backing him — accountable for policy. The prime minster and the party leaders in the majority coalition thereby have some incentive to govern responsibly.
But in the United States, voters choose a chief executive — a mayor, governor or president — independently of the legislature. So if voters hold the chief executive accountable, that alone does not ensure that government will act responsibly. It’s also necessary that voters hold individual lawmakers accountable.
Unfortunately, with STV, a typical voter does not get a specific representative to hold accountable. From our perspective, then, STV lawmakers lack incentives to tackle controversial issues realistically.
A more positive view of STV is available on the website of Fairvote, which refers to STV as "choice voting."