IMMORAL RELATIVISM. The Economic Policy Institute points out that Wisconsin public service employees are not, in the main, getting a better deal than private employees. "To get an apples-to-apples comparison," says Ezra Klein, "the study's author controlled for experience, organizational size, gender, race, ethnicity, citizenship and disability, and then sorted the results by education."

At National Review, Jim Manzi seizes on this as the study's fatal flaw, and tries to portray the study's original author, Jeffrey H. Keefe, as some sort of disingenuous leveller:

Stripped of jargon, what Keefe asserts is that, on average, any two individuals with identical scores on each of these listed characteristics “should” be paid the same amount.

But consider Bob and Joe, two hypothetical non-disabled white males, each of whom went to work at Kohl’s Wisconsin headquarters in the summer of 2000, immediately after graduating from the University of Wisconsin. They have both remained there ever since, and each works about 50 hours per week. Bob makes $65,000 per year, and Joe makes $62,000 per year. Could you conclude that Joe is undercompensated versus Bob? Do you have enough information to know the “fundamental personal characteristics and labor market skills” of each to that degree of precision?

Also, what if Joe really sucks at his job? Or what if Bob is actually worse at his, but has a winning personality and shoots skeet with the boss? See, if social science teaches us anything, it's that statistics are meaningless, if used by liberals.

Manzi claims Keefe does not take into account true "systematic differences in the market realities of the skills, talents, work orientation" between public and private employees, and made his findings "without adjusting for an all-but-infinite number of... relevant potential differences between the weight-average public-sector worker and the weight-average private-sector worker."

Manzi lists some of these differences ("Whether their years of education for the job are in molecular biology or the sociology of dance"), but never mind -- if you find that they still don't convince you that schoolteachers are worthless freeloaders, he can always cook up more. They're all but infinite!

And since Keefe didn't take all these infinitesimal gradations into account, says Manzi, his claims are "worse than useless; they are misleading."

The whole question — as is obvious even to untrained observers — is whether or not there are material systematic differences between the public and private employee that are not captured by the list of coefficients in his regression model.

You folks have probably caught on to what he means by systematic differences: The differences between his team and the other team. And as long as his team has a full tank of propaganda to run on, the pointy-heads can take a break.