Rob Richie and FairVote are notorious for hammering this point home and it’s one of the few valid points they make. League of Women Voters sites it in their analysis, and used it as the foundation of their anti-cardinal position in Oregon. I recently spoke with Professor Darlington from Cornell, who has a long history simulating methods and who advocates for Condorcet and he said something to the same effect. He regards it to be a deal-breaker, even though he thinks Score would otherwise be one of the best methods. He said that that’s the consensus in ordinal voting circles which are educated on voting theory.
With Score the best strategy is generally to give all your candidates min or max scores, while also being sure to max-score your lesser-evil if you don’t think your favorite can win. Essentially Approval voting on a Score ballot. This is explained in detail on Warren’s Smith’s site and it looks like this article (which I didn’t actually read) has the details. https://www.rangevoting.org/RVstrat.pdf
The point is also backed up by VSE simulations, which show that Score voting has the strongest strategic incentives second only to Plurality voting (Plurality is ~3x worse!) and that the incentives increase the larger the ballot scale.
Interestingly with Approval Voting, as with Plurality, the overall election results improve when voters are strategic. This is why most cardinal advocates who are familiar with it are not concerned by it. (This is the opposite of systems like STAR and Condorcet which are more accurate overall when voters are more honest.)
[Pgf. edited: 1st draft accidentally said Score instead of Approval here.]
Ideally we want a method which does not incentivize strategic voting, and which is also more accurate overall when voters are honest.
Most voting methods incentivize the type of voting behavior which produces the best outcomes, to varying extents. (STAR, and Condorcet are accurate with honest voting and honest voting. Approval and Plurality incentivize strategic voting and perform better when voters are strategic.)
[Edited, to remove Score from this section and add it below. 1st draft had it in the wrong category.]
A notable exception is IRV, which incentivizes strategic voting ~3:1 (according to the VSE graph on strategy works v. backfires) but which is more accurate when voters are honest. Luckily the strategy in RCV isn’t that obvious. That said I figured it out and others can too. Score Voting is also most accurate when voters are honest, but does not incentivize that behavior.
I want to end by stating that Score Voting is a great voting system. That it’s a lot better than Approval, and that this is the only valid concern with it, while most other methods have multiple issues which are worse than this.
This is also the reason that STAR was invented and why most Score fans love STAR. The runoff eliminates this strategic incentive or renders it more or less in-actionable.