This scholarly paper, where they take the time to adjust for education requirements and the kinds of thing that make up scientific study rather than journalism says that overall Fed works are paid, on average, 11% less than private workers.
In this study we found that state and local workers
are compensated less than their private sector counterparts.
We implemented a standard comparability
exercise, using the CPS and following common methodological
choices that reflect the heart of the discipline.
Our results of lower compensation for state and local
workers are consistent with previous findings, and we
expand on them. The differentials were evident by 2000
in the work of others, and the patterns identified have
either remained or grown since then. Although a comparison
of unadjusted average earnings will show that
wages are higher among jobs in state and local government,
this result is largely due to the fact that the
workers in those sectors have more education. Holding
education and other characteristics the same, typical
state and local workers earn an average of 11 percent
less and 12 percent less, respectively, than comparable
private sector workers.
http://www.nirsonline.org/storage/nirs/documents/final_out_of_balance_report_april_2010.pdf