- become more complex and
- it has become clear that a physician's case volume is negatively associated with their complication rate; that is, complications tend decrease as volume of cases goes up.
- McHenry CR (2002). "Patient volumes and complications in thyroid surgery". The British journal of surgery. 89 (7): 821–3. PMID 12081730. Full Text
- Birkmeyer JD, Finlayson EV, Birkmeyer CM (2001). "Volume standards for high-risk surgical procedures: potential benefits of the Leapfrog initiative". Surgery. 130 (3): 415–22. PMID 11562662.