Influencing physician referrals.

Primary care physicians have several external sources of information available when referring a patient to a specialist. The most-used sources were a fellow physician, followed by the specialist, the patient or the patient's family, and to a lesser extent, hospital-controlled sources including referral directories, call services, and sales representatives. The authors tested a cost-benefit model where source usage was predicted to increase as the costs of using the source decreased and benefits increased.