Great point!
The correspondence between theoretical and practical efficiency is definitely not perfect. Theoretical efficiency guarantees that individuals are properly incentivized. Practical efficiency may not follow because of things like computational costs, and the extent to which this will be a problem will depend on the specific mechanism and the situation in question. For example, in the computational cost case, the actions of large companies would probably be closer to optimal behavior than individual actions.
My hunch would be that proving theoretical efficiency is generally a relatively good proxy for practical efficiency in most cases, but these other practical considerations should be considered in addition to it, as further constraints that one is trying to satisfy. But this is an empirical question, and I’m also relatively uncertain here.
Thanks, David! My first reaction your points:
I don’t know, your guess is probably as good as mine here
I broadly agree with you about this point. The whole exercise of public good provision is trying to improve over the welfare level of private provision, but it’s not as if falling short from full efficiency makes a mechanism undesirable. Higher efficiency is one of the things we should aim for relative to existing solutions; perhaps the most important one, but not necessarily the dominant consideration, and improvements to various degrees seem valuable. I emphasize “full” efficiency in this writeup because it’s a major ground that’s given to justify the perspective that QF is promising.
Not quite sure I understand your point about it being a different extreme assumption. It is a generalization because the complete information case can be seen as a particular case of the setting we use. For example:
When every individual only has a single type
When only a single type occurs with positive probability
When types are perfectly correlated with each other