Does anyone know if there is data showing an average, expected, "normal" percentage of over-coding or under-coding found in a physician practice?

I have found a few articles where fairly widespread studies were conducted (e.g. 5 progress notes sent to providers to code, results compared to panel of certified coders). I know the goal is to be 100% right, though I do believe there is likely an "expected" amount of over and under-coding found.