The Ambulatory Sentinel Practice Network: purpose, methods, and policies.

The Ambulatory Sentinel Practice Network (ASPN) is a network of primary health care practices across the United States and Canada offering (1) a laboratory for the study of populations under the care of primary care providers, and (2) surveillance of primary care problems and services. This paper reports the methods and policies developed and used by ASPN to conduct studies and describes the initial sentinel practices.