Variations in the amount of surgery, according to a source cited in the text, seem to be a function of all but which of the following?

Question

Quizplus · Accepted Answer

Variations in the amount of surgery are influenced by factors such as the supply of surgeons, the availability of reimbursement, and the type of hospital, rather than strictly by the objective needs of a patient population. This suggests that external factors, rather than just medical necessity, can drive the frequency of surgical procedures.

Variations in the Amount of Surgery, According to a Source