This article examines the correlation between APRN's and PA"s and their workplace scopes. It discovered that in states with the highest shortage of Primary Care Physicians, APRN's and PA had a widened scope of practice. The shortages of physicians dramatically increased the abilities and scopes to which these APRN's and PA's could function in a clinical setting.
http://www.nejm.org/doi/pdf/10.1056/NEJM199411103311905