The participating practices included 49 PPRNet family practice offices. Founded in 1995 by the Medical University of South Carolina Department of Family Medicine, PPRNet is a practice-based research network based in Charleston, SC.6 Research activities of the PPRNet are based on a longitudinal patient database composed of data from electronic patient records. To participate in PPRNet, the clinic must use the Practice Partner Patient Record electronic medical record. The database is updated quarterly and contains demographic information, vital signs, diagnoses, medications, laboratory test results, and other data. As of October 1998, PPRNet practices are located in 24 states. Rural, urban, and suburban areas are represented. Currently, the PPRNet database has information on 479,192 patients, including 2.5 million patient contacts, 5.9 million diagnoses, 2.9 million prescriptions, 0.4 million allergies, 7.4 million vital signs, 10.2 million laboratory test results, and 1.0 million preventive services. From the PPRNet master database, a smaller database was created that included age, sex, height, weight, and date of visit for all 4- to 19-year-old patients visiting the practices from January 1995 through December 1997. We chose a 3-year time frame because most children visit their physician at least once in 3 years, allowing us to capture most of the children enrolled in these practices.