Let’s look at quit rates. Quit rates in the public sector are about one third what they are elsewhere. In other words, government employees sure do seem to like holding on to their jobs. More than just about anyone else, in fact. Doesn’t that tell us everything we need to know about who’s overcompensated?
I don't want everyone with a public-employee axe to grind running around shouting "definitive!" but this is certainly an intriguing way of looking at the issue.
Simply controlling for education doesn't definitively prove that the public sector employees are underpaid either, and that's the point.