Nurse practitioners have been promoted as a cost-effective way to meet this need. Medicare currently reimburses nurse practitioners only 85 percent of the amount that it reimburses primary-care physicians. Paying less for the same work would appear to be a way to save health care dollars.

But are nurse practitioners actually more cost-effective? There is a dearth of good recent empirical research on this question, but some studies have suggested that the answer is no. Nurse practitioners, though generally praised for being sensitive to patients’ psychological and social concerns, appear to order more diagnostic tests than do their physician counterparts. In one study, published in 1999 in the journal Effective Clinical Practice, primary-care patients assigned to nurse practitioners underwent more ultrasounds, CT scans and M.R.I. scans than did patients assigned to physicians. The nurse practitioners’ patients also had 25 percent more specialty visits and 41 percent more hospital admissions.

These differences are costly. According to the study, they “may offset or negate any cost savings achieved by hiring nurse practitioners in place of physicians.”