Bryce Carmony argues on Twitter that Score Voting is more vulnerable than Approval Voting to tactical nomination. His justification for this is:
My evidence is getting 10% of a vote is easier than getting 100% of a vote.
To make this claim clear and coherent, what I think he’s really trying to say is that changing the normalization boundaries is more likely to change relative scores than approvals. E.g. if you change my score for X from 0 to 2, that has no effect in Approval Voting because it’s a “disapproval” either way (assuming a threshold of 2.5 let’s say).
But the unproven assumption here is that this makes any difference on candidate behavior. If a tactical nomination is only half as likely to work with Approval Voting, so what? That might still be plenty of incentive. Or put another way, why would the incentive be big enough with Score Voting but not big enough with Approval Voting?
There are other factors. In a competitive election, where we already have a variety of candidates, and thus it becomes harder for tactical nomination to have any effect. You have to nominate increasingly more extreme candidates than yourself to convince voters you’re a safe choice. And if they’re using probability of winning in their approval threshold, then this won’t have much impact anyway, as those extremists are going to be deemed no-hopers.
I could go on.
I don’t think bullet voting is a very big issue, but to the extent some voters are irrationally optimistic, and thus willing to vote for their favorite, IoIA failure (and thus, vulnerability to tactical nomination) might actually be worse with Approval Voting. Let’s say 5% of voters might fall victim to this. That could easily be enough to wipe out any gains Bryce is speculating about here.
The larger point is that this is a higher speculative and complicated angle, and Bryce isn’t providing any arguments that pass the muster that most election theorists would put forth. Even for people who already prefer Approval Voting to Score Voting, and doubt many would find this particular argument compelling.