Variation in GPs' referral rates to specialists in internal medicine.

In this article multilevel analysis (MLA) is used in order to analyse a large data set on general practitioners' (GPs') referrals to specialists in internal medicine. The hypothesis is tested that patients' morbidity is the main determinant of GPs referral rates. From a Dutch survey among 161 GPs, referrals to specialists in internal medicine were selected. The results corroborate the main hypothesis: approximately half of the variation in the overall chance of being referred is associated with patient characteristics and approximately 45% with patients' morbidity measured in terms of the GPs' diagnosis. Referral chances differ mainly with diagnosis, which implies that the variation in the referral rates reflects a variation in case mix rather than differences in the quality of care or efficiency. The only doctor or practice characteristics that affect referral chances are the number of instruments available in a practice (more instruments, fewer referrals) and GPs' list sizes (larger lists, more referrals). (aut.ref.)