There's a very interesting back and forth between Jim Manzi and Ezra Klein about an EPI study purporting to show that Wisconsin's public sector unions are underpaid.  It's hard to sum up, but this excerpt encapsulates what I think is the core dispute:

Ezra Klein has responded to my post in which I argued that the EPI study that claimed to show that Wisconsin public sector workers were underpaid is unpersuasive. His response begins with this:

Jim Manzi has posted a critique of the Economic Policy Institute's study (PDF) suggesting that Wisconsin's public-sector workers are underpaid relative to their private-sector counterparts. It basically boils down to the argument that this sort of thing is hard to measure. The study controls for most every observable worker characteristic that we can imagine controlling for.

But my basic criticism was that it fails to control for lots of plausible, common-sense differences. That is, that the study doesn't control for all the characteristics we can imagine, but rather, some of those for which we happen to have data.

Klein is correct to say that my post "basically boils down to the argument that this sort of thing is hard to measure." But he then argues that the purpose of the original study was not to demonstrate that public sector workers are underpaid, but rather to rebut the claim that they are overpaid:

[T]he EPI study is aimed at a very specific and very influential claim: that Wisconsin's state and local employees are clearly overpaid. It blows that claim up.

That may have been the author's motivation, but here is the final conclusion of the executive summary of the report:

[P]ublic sector workers in Wisconsin earn less in annual or hourly compensation than they would earn in the private sector.

The report makes a positive claim that it has determined a compensation "penalty" for working in the public sector, and repeats it many times. My argument was that this report does not establish whether or not this claim is true.

It's obvious that this study doesn't control for everything we can imagine, because it doesn't even control for the matters that are of central dispute in Wisconsin: protection from being fired.  This is, as people on both sides keep noting, so extraordinarily valuable that workers are willing to give up quite a lot to get it.  And of course, a job that offers this sort of protection is likely to attract workers who especially value it.  All government jobs offer this perk, which is valuable to the workers and costly to the employers; ceteris paribus, I'd expect that other compensation would be lower to compensate.

Obviously, it also doesn't control in any way for other job or worker characteristics that effect compensation; jobs working for state and local government are systematically different from other sorts of jobs, because so much of what the government does isn't done by anyone else.  Though, oddly, for the teachers at the heart of this dispute, we do have a good comparison: private school teachers. And as I understand it, public school teachers have higher wages, and much better benefits, than private school teachers.

To which I expect the union's boosters will say, "But jobs in private school are much more enjoyable--they don't have to teach the difficult kids!"  Indeed, they're right.  Which is exactly the point: there's huge unobserved variable bias here.

There's also the fact that the EPI study seems to be looking at means, which are going to be dragged upwards by a small number of highly compensated workers, particularly in the educated group.  But state and local wages are capped.  Meanwhile, some of the highest paid jobs in the private sector are in areas like commission sales, which have no counterpart in government. That means that the median worker is probably making much more than the median worker in the private sector.  This may not be true in some lucrative fields such as law and medicine--but even there, we tend to compare government lawyers to the highly paid people at white shoe firms or corporations, not the legions of struggling will-drafters and ambulance-chasers.  

You can argue, of course, that this is an ideologically much more attractive income distribution.  Which highlights, I think, the core difference between the way people like Manzi and I look at this, and the way that progressives do.  I don't think of state employment as a way to create, in miniature, my ideal labor utopia.  I think of it as a way to procure services.  I define people as being "overpaid" not if they are paid more than someone with a similar level of education, but if they are paid more than I need to entice to pay to attract adequate workers.  To analyze that, looking at medians is probably somewhat more instructive than looking at means.

Of course I agree with Manzi that this still doesn't really tell us whether state workers are overpaid, underpaid, or just-right-paid.  I suspect that the answer is probably "both"--adjusting for worker quality, the median government worker is probably overpaid, while in skilled specialties, salaries are probably not attracting as much of the top-flight talent as we'd ideally like.  (This is why I have been advocating, futilely, that we make it possible to pay SEC employees multiples of what the President of the United States makes.)  But as Manzi, who does this stuff for a living, will undoubtedly tell you, setting compensation is a really hard problem that no one's got a very good handle on.  So that's just a suspicion, based on my experience of state bureaucracies, and my best guess at the incentive effects of the current structure.  I don't have enough data to back me up.  And neither does EPI.
