"A core problem is that the Bureau of Labor Statistics no longer conducts surveys designed to report the prevailing market pay for specific jobs. At one time BLS did conduct a so-called benchmark survey, reporting market rates nationally and in each locality area, but it was terminated in the mid-1990s.
That's when the problems started. No president has ever agreed to close the "pay gap" and there is no reason to believe that is going to change. Current BLS surveys were not planned for this purpose, and after trying for two decades, there is no reason to think complex statistical models will produce credible answers."