PT - JOURNAL ARTICLE AU - Frederick M. Chen AU - George E. Fryer, Jr. AU - Thomas E. Norris TI - Effects of Comorbidity and Clustering upon Referrals in Primary Care AID - 10.3122/jabfm.18.6.449 DP - 2005 Nov 01 TA - The Journal of the American Board of Family Practice PG - 449--452 VI - 18 IP - 6 4099 - http://www.jabfm.org/content/18/6/449.short 4100 - http://www.jabfm.org/content/18/6/449.full SO - J Am Board Fam Med2005 Nov 01; 18 AB - Objective: To examine the effect of patient characteristics and comorbidity on referrals in primary care.Methods: Cross-sectional analysis of patient encounters and referrals during a 1-year period for a primary care network of 9 clinics. The analysis adjusted for the clustering effect of physicians and clinics on the data.Results: 23,720 specialty referrals were generated from 251,240 patient encounters, resulting in a total referral rate of 9.4 referrals per 100 encounters. Age, gender, and certain comorbid conditions were significant predictors of referral for any given encounter.Conclusions: Patient characteristics and comorbidity are predictors of referral. Studies of primary care processes need to account for clustering of physicians and clinics in their research design.