In this section we explore how RCV has worked in practice in the United States. We summarize research on how many voters rank candidates and how those rankings are organized, on how RCV has worked to remove the spoiler effect and on the tendency of RCV in single-winner seats to elect candidates with majority support. We also assess RCV in practice on some more technical grounds, namely monotonicity and its tendency to elect Condorcet winners.
Experience shows that, when American voters are given the option, they prefer to rank candidates rather than merely lodge a single preference for one candidate. In the vast majority of RCV races contested by more than three candidates (the minimum number of candidates needed before ranking is meaningful), a significant majority of candidates rank at least two candidates.
For example, in 2014, three-quarters (74%) of Oakland voters ranked three different mayoral candidates (the maximum allowed). Another 11% of voters ranked two. In the 11 Alameda County RCV races that had three or more candidates in 2014, 63% of voters ranked three candidates, and 76% ranked at least two. Similarly, in the five-way contest for San Francisco’s 10th Supervisor District with a strong incumbent, only a third of voters ranked just one candidate – and only 8% of these were bullet voters (2% of all voters in the 10th District race) who voted for a candidate who failed to reach the final round.
Using ballot image data, we can do more than summarize how many candidates voters ranked. In multi-winner RCV, we can study how voters used their preferences. For example, in 2014, FairVote's Andrew Douglas used ballot image data to show a pattern of racially and ethnically cohesive voting among Cambridge, MA, city council voters. FairVote will soon release more research, showing the relative influence of candidate ideology, incumbency status, race, gender and place of residence on the choices made by Cambridge city council voters.
One of the chief potential advantages of single-winner RCV over plurality is that it mitigates the spoiler effect. With the mounting experience with single-winner RCV in the United States, empirical analysis of the spoiler effect in American RCV elections is now possible. Stay tuned for our findings.
The use of single-winner RCV should increase the proportion of candidates winning with a majority of votes cast and the likelihood of the winner being the Condorcet winner. FairVote is currently using ballot image data to research the relative tendencies of single-winner RCV and plurality to elect majority and Condorcet winners -- the candidate who theoretically would defeat all others in a one-on-one race.
Monotonicity is a technical property of a voting system in which it is impossible for a voter to prevent the election of a candidate by ranking them higher on their ballot while also being impossible to elect an otherwise unelected candidate by ranking them lower. In the absence of monotonicity, a voter may hurt the chances of their most favorite candidate winning if they ranked the candidate first rather than second on their ballot. RCV is non-monotonic but in practice should rarely behave non-monotonically. FairVote is currently using ballot image data to explore whether single-winner RCV has ever behaved non-monotonically in the American experience.