Special Article

Physicians' Responses to Financial Incentives — Evidence from a for-Profit Ambulatory Care Center

David Hemenway, Ph.D., Alice Killen, M.B.B.S., M.P.H., Suzanne B. Cashman, Sc.D., Cindy Lou Parks, P.A., M.S., and William J. Bicknell, M.D., M.P.H.

N Engl J Med 1990; 322:1059-1063April 12, 1990

Abstract

Abstract

Health Stop is a major chain of ambulatory care centers operating for profit. Until 1985 its physicians were paid a flat hourly wage. In the middle of that year, a new compensation plan was instituted to provide doctors with financial incentives to increase revenues. Physicians could earn bonuses the size of which depended on the gross incomes they generated individually.

We compared the practice patterns of 15 doctors, each employed full time at a different Health Stop center in the Boston area, in the same winter months before and after the start of the new arrangement. During the periods compared, the physicians increased the number of laboratory tests performed per patient visit by 23 percent and the number of x-ray films per visit by 16 percent. The total charges per month, adjusted for inflation, grew 20 percent, mostly as a result of a 12 percent increase in the average number of patient visits per month. The wages of the seven physicians who regularly earned the bonus rose 19 percent.

We conclude that substantial monetary incentives based on individual performance may induce a group of physicians to increase the intensity of their practice, even though not all of them benefit from the incentives. (N Engl J Med 1990;322:1059–63.)

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Media in This Article

Table 1Changes in Practice Patterns among 15 Full-Time Physicians after the Institution of Financial Incentives at an Ambulatory Care Center.*

Table 2Changes in Practice Patterns among the Physicians, According to Whether the Physician Never or Always Received the Bonus.*

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Article

PREVIOUS investigations have examined the responses of physicians to monetary incentives.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 However, only a few of these studies have focused on ambulatory care,8 9 10 11 12 13 14 15 16 17 18 19 fewer still have dealt with diagnostic testing in an outpatient setting,11 12 13 14 15 16 17 18 19 and there appear to have been no formal analyses of the effects of monetary rewards on the behavior of physicians in investor-owned clinics operated for profit. The number of such centers grew rapidly in the 1980s, and the pressure from management to increase revenues has been the subject of some controversy.20 , 21

One limitation of many previous studies of the responses of physicians to financial incentives is that the researchers have often been forced to compare different doctors working in different facilities and seeing different patients. We report on a natural experiment over a one-year period at a chain of walk-in centers providing ambulatory care. The doctors were the same, the available staff and equipment were the same, and the patients, we believe, were similar. The only dramatic change was in the method by which the physicians were compensated.

Methods

Health Stop is a chain of investor-owned ambulatory care centers. Founded in 1983, it provides primary medical care in a consumer-oriented setting. The centers emphasize convenience for the patient: most are open every day of the year, and appointments are not necessary. Laboratory and x-ray facilities are located on the premises. From 1984 to 1986, when this study was done, some 20 centers were in operation, all in the greater Boston area. Most were staffed by two full-time physicians, who each worked shifts of approximately 40 hours per week. (By 1989, Health Stop had become the largest chain of its kind, with 120 centers in 11 cities, including 33 centers in New England.)

Until 1985, physicians working for Health Stop were paid at a flat rate of $28 per hour. In the middle of 1985, a payment system involving bonus incentives was instituted, according to which physicians would receive either a flat fee ($28 to $32 per hour, depending on the physician's age and experience) or a percentage (24 percent up to $24,000 and 15 percent thereafter) of the gross monthly charges they generated, whichever was higher.

We compared the services provided and the charges generated by 15 physicians, each of whom worked at a different Health Stop center, during two three-month periods, from November 1984 through January 1985 and from November 1985 through January 1986. These 15 physicians were the only physicians to work full time at Health Stop during both periods. Six were family practitioners, eight specialized in internal medicine, and one specialized in emergency medicine. Fourteen were graduates of U.S. medical schools, and six were board-certified. Most were between 31 and 39 years of age.

Data were collected on each physician's gross charges, the number of patient visits, the number of hours worked, the number of x-ray films ordered, and the number of laboratory tests ordered each month. Tests administered as a group, such as a complete blood count, were counted as a single test. To account for the effect of inflation, we constructed a price index for changes in the prices of services provided at Health Stop between December 1984 and December 1985. For each period studied, the prices of nine of the most common services (such as an initial visit, a return office visit, urinalysis with microscopy, complete blood count, and two-view chest radiography) were weighted according to the number of times each service was delivered by Health Stop providers from November 1984 through January 1985.

We used a paired t-test to determine the statistical significance of the changes in the physicians' patterns of practice. The data about each physician for the period from November 1984 through January 1985 were matched with the comparable information for the same period 12 months later. Thus, each physician acted as his or her own control. (Because of the small sample, we also tested for significance by the Wilcoxon signed-rank test; the results were virtually identical.)

We also compared the practice patterns of physicians who generated sufficient charges to receive a bonus with those of physicians who did not. Our interest was in determining why the latter group produced low levels of revenue and whether both groups increased the intensity of their practices over time.

Results

After the institution of the bonus system, the Health Stop physicians increased the number of both laboratory and radiographic tests ordered per patient visit. Eleven of the 15 doctors ordered more x-ray films per visit; for the entire group, the number of x-ray films per visit increased 16 percent (Table 1Table 1Changes in Practice Patterns among 15 Full-Time Physicians after the Institution of Financial Incentives at an Ambulatory Care Center.*). (Nationally, the number of x-ray films ordered per office visit by ambulatory care physicians increased by 2.2 percent per year from 1981 through 1985.2) Thirteen of the 15 doctors at Health Stop centers ordered more laboratory tests per visit; as a group, the 15 ordered 23 percent more tests per visit. (Nationally, comparable data are available only for Pap smears; the number of these increased by 3.2 percent per year from 1981 through 1985.22)

In the one-year period, the number of office visits per month increased by 12 percent, average charges per visit by 15 percent, and total charges per month by 28 percent. (Nationally, the number of visits to physicians' offices increased 3.7 percent per year from 1983 through 198523 , 24; the total revenues of general and family physicians rose 8 percent in 1984 and 1985.25) Part of the dollar increase at Health Stop was due to higher prices. The price index we constructed showed that the average price at Health Stop increased 6.8 percent between December 1984 and December 1985. (In 1984 and 1985, the medical care component of the national consumer price index rose 6.3 percent.26) Therefore, at constant 1984 prices, the real charges for services per visit for these 15 Health Stop physicians increased 7 percent, and the real charges per month increased 20 percent.

Six physicians generated enough revenue for the volume incentive to take effect every month of the study. By contrast, seven never created sufficient charges to earn the bonus and thus received the flat hourly wage each month. These two groups are compared in Table 2Table 2Changes in Practice Patterns among the Physicians, According to Whether the Physician Never or Always Received the Bonus.*. The remaining two physicians earned bonuses during some but not all months in the study period and were excluded from this analysis.

The intensity of practice in both groups increased over time. The increase in charges per month in the two groups was quite similar — 16 percent and 18 percent, adjusted for inflation — although it was achieved as a result of somewhat different changes in practice patterns (in the group receiving the bonus, the number of x-ray films per visit rose more than the number of laboratory tests; in the no-bonus group, the number of laboratory tests per visit rose more). However, the changes in practice patterns within each group were not statistically significant, possibly because of the small size of the groups.

The differences between the two groups in monthly charges generated per physician were primarily the result of differences in the number of patients seen. Although in both groups the number of patient visits per month increased by about the same amount, the group receiving the bonus had more patient visits at base line (352, as compared with 246 visits per month in the no-bonus group), despite working a similar number of hours. Thus, after the bonus system was instituted, the group receiving the bonus had 378 patient visits monthly, as compared with 276 in the other group. Over 80 percent of the increased total charges in the bonus group were due to this higher volume of patient visits. The two groups differed significantly from each other both before and after the bonus was instituted only in terms of patient visits per month and total charges per month. The dollar bonus for the six physicians was substantial: it increased their monthly income by almost $800, a 19 percent increase.

Discussion

As an investor-owned, for-profit company, Health Stop has a primary goal of increasing its revenues faster than its costs. However, in the first few years of the company's operation, the Health Stop doctors were paid a flat hourly wage. As compared with fee-for-service practitioners, individual physicians at Health Stop had few salary incentives to "build the practice" or increase the amount of revenues per patient. Health Stop therefore modified its system of compensation to bring it more into line with the incentive structure found in many solo or small-group practices.

One method of evaluating the work of physicians at Health Stop involved the preparation of monthly reports that ranked physicians according to the average charge per patient visit and the number of diagnostic tests performed. Managers then questioned individual doctors for whom these figures seemed extreme in either direction — doctors who appeared to order either too many or too few laboratory tests and x-ray examinations. Physicians who refused to modify general patterns of practice that did not meet the company's standards of quality were fired.27

We do not know whether the increased number of diagnostic tests was medically justified in the 15 physicians studied. However, the evidence suggests that salaried doctors may treat patients less aggressively than fee-for-service physicians.5 , 10 , 16 , 18 At free-standing clinics in Texas, physicians paid on an hourly basis ordered markedly fewer diagnostic procedures than a nationwide sample of physicians.28 29 30 More particularly, a review of the medical records of more than 800 patients seen at Health Stop clinics in 1986 (after the start of the bonus system) in five diagnostic categories found little evidence of gross overtreatment.31 For example, in an audit of the records of treatment provided to patients with pharyngitis, only 4.4 percent of the patients had been given unnecessary blood tests to rule out infectious mononucleosis. Of 138 patients with open wounds, 10 percent had received immunizations for tetanus that were not indicated. By comparison, in a study of the treatment provided in six emergency rooms, 17 percent of patients with open wounds were overtreated with prophylaxis against tetanus.32

It has been claimed that "the way physicians are paid affects the services they provide."33 The empirical evidence, however, is fragmentary and sometimes inconsistent. Many studies have contrasted the practice styles of physicians in health maintenance organizations with those in fee-for-service settings.1 , 2 , 12 13 14 , 16 17 18 With respect to radiographic and laboratory testing, some studies have found that more testing is done in prepaid group practices,12 , 13 others have found that there are more tests when physicians are paid on a fee-for-service basis,18 and still others have found similar patterns of testing in the two settings.14

Various studies have examined how changes in the method of paying physicians affect their patterns of practice.3 , 4 , 6 7 8 9 , 11 , 15 Some have found positive associations between changes in the level of payment and the intensity of the practice,6 , 7 one a negative association,15 and some no relation.3 , 4 , 9 When no relation has been found, the suggested explanations have been that the financial incentives were too small3 , 9 or that they were keyed to collective rather than individual performance.9 All the investigators had difficulty isolating the specific effect of the system of physician payment; the differences in practice style may have been caused instead by such other factors as differences in the characteristics of patients and physicians, organizational structure, group size, or the availability of equipment. In the methodologically cleanest study, physicians serving as residents in a single clinic were randomly assigned to receive either salary or fee-for-service reimbursement10; the latter scheduled more visits per patient and saw their patients significantly more often than the former. Unfortunately, differences in revenue generation and testing practices were not reported.

We analyzed changes in the patterns of diagnostic testing and practice among ambulatory care physicians working in the same offices during the same winter months one year apart. We believe that the characteristics of the patients seen during both periods were similar, although it has been suggested that as clients gain confidence in the new walk-in centers, they may return with more serious problems.25

Several limitations of the study deserve mention. Because we examined only 15 Boston-area physicians employed by a single organization, extrapolation of our findings may not be warranted. In addition, because there was no concurrent control group, changing environmental factors (such as the malpractice climate)34 may account for some of the observed results. Yet the increased rate of diagnostic testing and the higher charges per patient at Health Stop far surpassed the national averages with respect to such changes in practice patterns, suggesting that particular factors may best explain our findings.

We are not sure why there was so much variation in the monthly number of patient visits among physicians working similar numbers of hours. In any case, all physicians in this study, including those who never received a bonus, increased the intensity of their practices after the bonus system was instituted. There are a number of possible explanations for these increases. First, only as the month drew to a close might individual physicians know whether they were likely to generate sufficient charges to receive the bonus. The monthly charges tended to be highly variable. For example, 2 of the 15 physicians earned the bonus during some but not all of the three months in the study period. Among the seven physicians who never received a bonus, one had monthly charges during this period that ranged from $10,966 to $18,716; another generated $12,890 one month and $19,581 the next (of these, both worked more than 40 percent more hours in the month for which their charges were higher). On a questionnaire,35 another of the seven physicians who never received the bonus reported that "the volume incentive never kicked in; we were never quite busy enough."

A second possible explanation for the increases is that the incentive system of payment gave a signal to all physicians of how strongly the Health Stop management cared about the generation of revenue. The corporate emphasis on financial matters was presented in terms clearly understandable to all physicians working for the company. Finally, if physicians with high volumes of patients increased their charges per patient, doctors with low volumes who did not alter their practice patterns would become more conspicuous and more likely to be seen by managers examining the monthly rankings of physicians as burdensome and nonproductive.

Overall, our study suggests that substantial financial incentives that are based on the performance of individuals can lead ambulatory care physicians to alter their practice patterns. The management of Health Stop had always urged physicians to increase revenues. The only apparent change in 1985 was the creation of the new compensation system. The system of monetary rewards appears to have led virtually all the physicians to increase the number of patient visits and the rate of diagnostic testing.

Supported in part by a grant (HS05501) from the National Center for Health Services Research and Health Care Technology Assessment.

We are indebted to Health Stop Medical Management for its full cooperation with and support of this project, and to Dr. Cathie Spino, Ms. Sara Solnick, and Dr. Arnold Epstein for help and advice.

Source Information

From the Harvard School of Public Health (D.H., A.K.) and the Boston University Health Policy Institute (S.B.C., C.L.P., W.J.B.), Boston. Address reprint requests to Dr. Hemenway at the Department of Health Policy and Management, Harvard School of Public Health, 677 Huntington Ave., Boston, MA 02115.

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