Add up each physician's net collections. Subtract group-wide expenses equally among all physicians. Subtract direct department expenses equally among the physicians in a given department. These include clinical and clerical staff. Subtract other expenses by usage.
Allocations here are fairly complicated.
For instance, medical record costs are allocated by office visits. Billing is allocated by patient accounts. Human resource costs are allocated by the number of employees in a department. A department's rent is allocated by the space it uses. The net result is each physician's pay.