title: Effects of comorbidity and clustering upon referrals in primary care.
abstract: 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.
authors.affiliation: Department of Family Medicine, University of Washington, 4311 11th Avenue NE, Ste. 210, Seattle, WA 98195, USA. fchen@u.washington.edu
authors.forename: Frederick M
authors.initials: FM
authors.lastname: Chen
authors.forename: George E
authors.initials: GE
authors.lastname: Fryer
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Norris
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000553:Ambulatory Care; D015897:Comorbidity; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008511:Medicine; D008875:Middle Aged; D011320:Primary Health Care; D012017:Referral and Consultation / Q000458:organization & administration*; D013038:Specialization; D014861:Washington