Does Meek STV Incentivise Strategic Voting?

Question

I have recently looked at the explanation of the Meek Single Transferable Vote method of elections, and it seems like it's a rather multi-step algorithm.

Now, a major reason for STV systems seems to be an attempt to reduce perverse incentives of the strategic sort. However, after looking through the explanation, I'm not sure whether that goal is being achieved or not with MSTV.

And it would probably take looking through a bunch of use cases to check that (and spend some time figuring out whether one 'buys' some of the premises on which the arrow theorem is built). But surely someone has already done that.

And since it was already done by someone else, I'd like to ask what the results/conclusions are. Is strategic voting 'a thing' in MSTV? Are there 'tricks' to assigning (or not!) numbers to candidates one doesn't want to win at all in MSTV, or not?

Answer 1

_{Note: for anybody wondering how Meek STV works, see this and this}

Tl;dr

Yes, it incentivizes strategic voting

Arrow’s impossibility theorem

Arrows impossibility theorem says that no voting system can ever be “fair” (for certain definitions of “fair”)

How to strategic vote

Let’s say we have 3 candidates. Let’s have C1, C2, and C3. They are running for an election with two winners, and the election uses the Meek STV voting process. Now we have you, the voter. You want C1 and C2 to win the election. You believe that C1 is going to win, regardless of whether you vote for them or not. You believe that C2 and C3 will get similar scores.

Here are two sensible ways to vote:

1. C1, C2, C3
2. C2, C1, C3

If you choose option 1, and C1 wins, your vote for C2 will count as a fraction.

If you choose option 2 , your vote for C2 will count for the full amount (or however much amount is necessary for C2 to win).

Therefore, if you know C1 will win, and you want C1 and C2 to win, it is better to pick option two, and vote: C2 as first choice, C1 as second choice, C3 as third choice. This is true even if you want C1 more than C2.