Free riding

Free riding is a form of tactical voting which exists in all multi-winner systems. The basic strategy is to not vote for all of the candidates you support since you expect other to elect them. This is a particularly useful strategy when those who elect them for you do not support those you do vote for. The existence of this strategy is a by product of mechanisms used to increase proportional representation.

Types

Vote Management

Vote management is when multiple people collectively decide how to vote to optimize the ability to free ride.

In Specific systems

Immune systems

Many systems are not susceptible to free riding. All Single Member District systems, such as Single Member Plurality are immune to Free Riding. Similarly so are Bloc voting. This is because these systems have no mechanism designed to improve Proportional Representation.

Multi-Member Systems

Systems with Hare quotas have greater incentive to Hylland free ride / manage votes than ones with Droop quotas. Single transferable vote elections nearly always use Droop quotas, but the fact that the votes are transferable takes the risk out of free riding. However, in Multi-Member Score voting system like [Reweighted score voting]] it is riskier to free ride than ranking because they do not transfer votes but reweight. So there are two factors pushing in opposite directions. Multi-Member Score voting with Droop quotas would be better than STV, but that might also harm the system in honest cases. Most STV rules (i.e. not Meek) are also susceptible to Woodall free riding, though that is not useful for vote management.

Party-list proportional representation

In a pick-one party list election, there would still be a risk of poorly dividing your voters and losing seats compared to if you hadn’t tried it at all. I believe that there are only two jurisdictions that use this method for elections without also adding a threshold: Namibia and Hong Kong. (A threshold makes vote management much harder and much less effective, so while it might sometimes be mathematically possible, in practice it won’t happen.) Namibia is a one-party dominated state. The National Assembly elections that use the method elect all 96 seats in one nationwide electoral district. Last time, the largest party got 80% of the vote. Vote management is not practiced, and it wouldn’t matter.

In Hong Kong, there are multi member districts with 5, 6, or 9 seats. Vote management is very common. There are several pro-democracy and pro-Beijing parties, and parties often run multiple lists in a district, and divide their voters geographically. No single list has won multiple seats in the past two cycles. In effect, it is SNTV. It should be noted that not all the seats are elected by the general public, half are elected in “functional constituencies” that are conveniently divided in a way that heavily favors the pro-Beijing wing. Even more conveniently, these seats are elected by winner take all methods like FPTP, RCV, or in one case, PAL, while the seats elected by the general public, which opposes the pro-Beijing groups by ~60-40, use PR. So these elections have limited power over policy.

In practice, vote management in score methods with list cases of largest remainder would likely involve bullet voting for individuals and so look similar to vote management in Hong Kong. Vote management would be more essential in Monroe and allocation than SSS, because voters giving midrange scores to candidates are less likely to contribute to the quota in those systems; the candidate’s strongest supporters pay as much as possible first. This means that a party that doesn’t do any vote management will probably pay full quotas for their first seats, since a party nominee’s strongest supporters are likely to be partisans. In contrast, with SSS, midrange supporters for a candidate pay some of the cost, so the base of the winning candidate’s party will not pay the entire Hare quota even without vote management.

Further Reading

http://9mail-de.spdns.de/m-schulze/schulze2.pdf