A Randomized Trial - NCBI

Effect of a Gatekeeper Plan on Health Services Use and Charges: A Randomized Trial DIANE P. MARTIN, PHD, PAULA DIEHR, PHD, KURT F. PRICE, MS, AND WILLIAM C. RICHARDSON, PHD Abstract: A randomized trial was conducted to determine the effectiveness of a health care plan which uses physicians as gatekeepers to control health services use and charges. New enrollees in United Healthcare (UHC), an independent practice association, were randomly assigned to the standard UHC plan requiring a gatekeeper, or to an altemate plan with equal benefits but without a gatekeeper. Individuals in both plans were similar in demographic characteristics, perceived health status, and other health insurance coverage. The gatekeeper plan had 6 percent lower total charges per

enrollee than the plan without a gatekeeper. There were minor differences in hospital use and charges. Ambulatory charges were $21 lower per person per year in the plan with a gatekeeper (95% CI = -39.9, -2.1) and these were due to .3 fewer visits to specialists (95% CI = -0.50, -0.10). We conclude that a health plan which incorporates incentives and penalties for physicians to act as gatekeepers can reduce the cost of ambulatory services by limiting specialist visits. (Am J Public Health 1989; 79:1628-1632.)

Introduction Many health plans use a variety of mechanisms to encourage primary care physicians to act as "gatekeepers" in managing the medical care of their patients." 2 Incentives and penalties presumably will control cost by changing the gatekeeper's own practices and by limiting inappropriate hospital and referral care. The effectiveness of gatekeeper plans depends on the ability of participating physicians to coordinate the medical care system efficiently. Gatekeepers are used by many health maintenance organizations (HMOs), independent practice associations, preferred provider organizations, and some Medicaid plans," but evidence that they save money is lacking.5 Descriptive data exist showing that gatekeepers can decrease the use of services if the physicians share financial risk of providing care,6-" but there are no data from controlled studies. We therefore conducted a randomized trial of a plan using primary care physicians as gatekeepers to control health services use and charges. We randomly assigned study participants to United Healthcare, an independent practice association using gatekeepers, or to Northwest Healthcare, a plan with the same benefits but no gatekeeper. Because the economic incentives in the gatekeeper plan encouraged use of the gatekeeper and discouraged hospital and referral care, we expected that United Healthcare would have fewer hospitalizations, fewer visits to specialists, and lower use of procedures.

in the experiment and complete an initial telephone interview. Retirees were excluded from the study. The 90 percent of subscribers (families) who agreed to participate were assigned to a health plan according to a randomization scheme stratified by previous health care plan and type of employer, because State health insurance information showed that use of services differed significantly for these subgroups.9 Previous health care plans were: Blue Cross of Washington and Alaska, which provided comprehensive inpatient and outpatient coverage; Group Health Cooperative of Puget Sound, a staff model HMO; or no previous State health plan, for new employees. The two types of employer were: an institution of higher education, or other State agency. We assigned 555 subscribers and their dependents (1,419 enrollees) to the standard United Healthcare plan with a gatekeeper and 558 subscribers (1,408 enrollees) to the plan without a gatekeeper, Northwest Healthcare.

Methods Population and Random Assignment

United Healthcare (UHC) was one of three health care plans available to Washington State employees in the Seattle metropolitan area during the 1979 open enrollment. All subscribers (n = 1,239) and their family members who enrolled in UHC for the first time were asked to participate From the Departments of Health Services and Biostatistics, School of Public Health and Community Medicine, University of Washington, Seattle. Address reprint requests to Diane P. Martin, PhD, Associate Professor Department of Health Services, SC-37, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195. Dr. Richardson is currently Professor, Milton S. Hershey Medical Center, Pennsylvania State University; Mr. Price is Deputy Director, Health Services Cost Review Commission, Baltimore, MD. This paper, submitted to the Journal October 7, 1987, was revised and accepted for publication May 22, 1989. © 1989 American Journal of Public Health 0090-0036/89$1.50

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The Two Plans

Both plans were offered by the SAFECO Insurance Company and had the same insurance premiums and benefits. Premiums for the subscriber and all dependents were paid in full by the State. Both plans provided inpatient, outpatient, and preventive care coverage with copayments and limits on maternity and mental health services. There was no deduct-

ible or coinsurance, but there were copayments of $2 for each prescription and $25 for each general physical examination. The plan with a gatekeeper, United Healthcare, attempted to contain costs by enlisting primary care physicians in private practice as gatekeepers. The details of this plan have been published earlier.'O When the present study began, most gatekeepers had been in the plan for two years. Hospitalization and other major procedures entailed no utilization review, prior authorization, or mandated second opinions, and there was little emphasis on quality assurance or provider education. Because gatekeepers had only 25 plan patients on average, capitation reimbursement was not practical, and almost all were reimbursed at 95 percent of their charges. Thus, primary care physicians had no financial incentive to limit costs of the care they provided. There were stronger incentives for gatekeepers to mon-

itor referral care. In 1979, referral care consumed 74 percent of the amount paid for health services by United Healthcare.9 A risk-sharing account was established for each gatekeeper based on the age and sex of his or her panel of enrollees. These funds were then used to cover hospitalization, drugs, specialty, ancillary, and other referral costs. Catastrophic AJPH December 1989, Vol. 79, No. 12

GATEKEEPER EFFECT ON HEALTH SERVICES USE, CHARGES costs greater than $5,000 per patient were paid by a reinsurance program. At the end of the year, the gatekeeper shared with United Healthcare any deficit or surplus remaining in the account. If there was a surplus in the account at the end of the year, it was split equally between the gatekeeper and UHC. If there was a deficit, the gatekeeper had to pay back what was over-spent, up to an amount equal to 10 percent of his fee-for-service charges. The financial risk was not great to the physician. If the account was overdrawn, the minimum reimbursement rate was 85 percent (95 percent initial payment minus 10 percent), which was considered to be a reasonable return on charges. Furthermore, the risk applied to only a small proportion of the physician's total practice.

UHC gatekeepers could refer patients to the specialists could be made only to professionals such as optometrists, psychologists, chiropractors, and occupational and physical therapists. There were no financial incentives for specialists, non-physicians, or hospitals to practice efficient care, because they were paid 100 percent of their fee-for-service charges. United Healthcare required each enrollee to select a primary care physician from a list (N = 391) of family or hospitals of their choice. Referrals a few types of non-physician health

physicians (46 percent), internists (22 percent), pediatricians (19 percent), obstetrician/gynecologists (11 percent), and the few general surgeons (2 percent) who had joined the plan as gatekeepers. The gatekeeper was responsible for providing primary care and coordinating referrals for specialty care, ancillary services, and hospitalization. If the enrollee received care from a specialist or visited an emergency room for non-urgent care without approval from the gatekeeper,

UHC would not pay the claim and the enrollee was responsible for payment. Enrollees in the plan without a gatekeeper, Northwest Healthcare, were not required to choose a gatekeeper or to obtain approval for hospitalization, emergency, or specialist visits. These enrollees could receive care from any physician or non-physician health care provider in the Seattle area and the plan would reimburse the provider 100 percent of charges. Many of the same physicians who joined United Healthcare as risk-sharing gatekeepers also saw patients in Northwest Healthcare and were reimbursed in full for charges by that plan. Whereas physicians' offices submitted all claims to United Healthcare, Northwest Healthcare enrollees were required to submit claims to the plan for payment. Northwest Healthcare enrollees were provided with addressed, stamped envelopes to facilitate claims submission. Data Collection

The adult who made most of the health care decisions for the family was asked to complete a baseline telephone interview. Information obtained from the interview included family composition, demographic information, perceived health status, health insurance coverage, and usual source of health care. This information was used to stratify the random assignment to plans and assess the similarity of the two groups. Enrollees in both plans were followed for 12 months. Data on the use of health services and charges were collected from SAFECO computerized membership and claims records. At the end of the study, a questionnaire was mailed to participants to assess experience with the plans and other health insurance during the previous year and to ascertain out-of-pocket expenditures and satisfaction with the plans. The response rate for the mail questionnaire was 95 percent for each plan. AJPH December 1989, Vol. 79, No. 12

Charges and Use of Services We examined charges, percentage of enrollees using any services, and volume of services overall and separated according to primary care physicians versus specialists; ambulatory versus hospital care; type of procedure; and diagnostic category. We partitioned the enrollees into nonusers and users of services as described by Duan, et al," to separate differences in access to care from the effect of gatekeeper control once someone had entered the system. Total billed charges for 12 months were calculated for each enrollee, including all charges by primary care providers, specialists, hospitals, and ancillary services. Billed charges, rather than the amount paid by SAFECO, were used to ensure comparability between plans. Payments for coordination of benefits were not taken into account. We measured the percentage of enrollees using any services or a specific service during the study. We also measured the volume of services used per enrollee or per user, e.g., number of ambulatory care visits, hospital admissions and days. Definition of Primary Care Physician A physician was designated as a primary care physician (PCP) if he or she was a general or family practitioner, osteopath, pediatrician, general internist, or obstetrician/ gynecologist. All other physicians were defined as specialists. Although we tested two other PCP definitions with similar results, we used this definition to make primary care physicians as similar as possible in the two plans. This was the most conservative definition because it tended to overestimate primary care physicians in the plan without a gatekeeper and therefore any differences in primary care physician use between the two plans would be underestimated. Characteristics of Enrollees

Data obtained during the baseline telephone interview showed enrollees in the two plans to be similar in demographic characteristics, social structural variables, other insurance coverage, perceived health status, and usual source of health care (Table 1). Enrollees in the gatekeeper plan were more likely to have had internists, obstetrician/ gynecologists, or other specialists as their usual source of care. Assuming that care by internists and specialists is more costly than care by family physicians, this difference between groups might reduce the difference in cost between the two plans. On the other hand, internists or obstetrician/ gynecologists might be able to handle problems that a family physician would refer to a specialist. Analysis The differences in the means or proportions of outcome measures and the 95% confidence intervals around those differences were calculated. Analysis of covariance was used to adjust for the control variables. In general, the plan differences remained significant after controlling for main and independent variables for all enrollees and for users.9 Although there were few differences between the plans on key independent variables, many independent variables were significantly related to charges in both plans. Including these independent variables in the analysis did not change the findings of the univariate analysis in any substantial way, confirming the success of the randomized design. Because the adjusted and unadjusted results were essentially the same, the unadjusted rates are presented in this paper.* *Data available on request to author.

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MARTIN, ET AL. TABLE 1-Selected Characteristics of Enrollees in Gatekeeper or No Gatekeeper Plans*

Results Use and

Gatekeeper Characteristics Age (years) 0-5 6-17 18-44 45+

Mean (years) S.D. Percent Female Relationship to Subscriber Subscriber Spouse Dependent Family Size Mean number S.D.

Subscriber Years of Education Mean years S.D.

(n = 1419)

No Gatekeeper (n = 1408)

8.3%

9.2% 24.3 52.8 13.7 26.9

24.6 50.7 16.4 27.7

15.8 53.8%

53.7%

16.0

39.1% 22.6 38.3

39.6%

2.6 1.5

2.5 1.5

15.6 3.2

15.7 3.1

15.1 2.9

14.8 2.9

15.1% 43.1 25.8 16.0 27.9%

41.4 26.1 16.4

73.6% 23.0 3.3

74.0% 23.4 2.2

.1

.4

82.9%

84.2%

45.4%

49.5%

49.6% 22.7 13.9 8.0 5.8

21.7 9.5 6.2 5.5

10.5 2.2

10.3 2.3

21.3 39.1

Spouse Years of Education Mean years S.D.

Family Income Under $1 0,000

$10,000-20,000 $20,000-30,000 Over $30,000 Other Health Insurance Coverage

Perceived Health Status Excellent Good Fair Poor Had a Usual Source of Care before Study Period Usual Source of Care Was a UHC gatekeeper Specialty of Usual Source of Care before Study Period Family/General Practitioner Pediatrician Internist

Obstetrician/Gynecologist

Other

Months Membership in Plan During Study Mean months S.D.

16.2% 27.5%

57.1%

*Other characteristics which were measured but are not presented here due to small differences between plans include: marital status, family composition, family heaith nsk scale, employment status, months residence in community, and type of health insurance coverage.

Charges for All Enrollees Access to care, as reflected by the percentage of enrollees using any services or having at least one ambulatory visit, was high in both plans (Table 2). People in the gatekeeper plan had more visits to a primary care physician (difference = 6%, 95% CI = 2.43, 9.57) and fewer visits to a specialist (difference = -9%, 95% CI = -12.28, -5.72). Ambulatory charges per enrollee were $21 lower in the gatekeeper plan (95% CI = -39.9, -2.1, Table 3), due to significantly fewer visits to specialists. There were minor differences between plans in hospital use and charges per enrollee (Tables 2 and 3). The gatekeeper plan had lower hospital use than the no gatekeeper plan (Table 4). The plans had similar inpatient charges for specific services, such as medical, surgical, laboratory, and radio-

logical procedures (data not shown).*

Charges and Visits for Ambulatory Care We examined the effect of the gatekeeper plan among those people who used ambulatory services. PCP ambulatory visits and charges for users were similar, but users in the gatekeeper plan had significantly fewer visits to specialists and lower specialist charges (Table 5). There were no differences between plans in primary care physicians' use of surgical, laboratory, or radiological procedures, as defined by categories of Current Procedural Terminology codes (data not shown). PCPs in the gatekeeper plan ordered or performed fewer medical procedures on their patients than did PCPs in the no gatekeeper plan (difference = -4%, 95% CI = -5.13, -2.87). Specialists in both plans had similar use and charges for various types of procedures. We also compared ambulatory use between plans for 20 common diagnostic categories and found that people in the gatekeeper plan had fewer visits for mental health problems, back problems, and acute and chronic respiratory problems, and more of their visits for these problems were with a PCP rather than a specialist (data not presented).* Experience Using the Plans The end-of-study survey showed no difference between plans in enrollees' use of other health insurance plans, in the proportion of claims submitted, or in out-of-pocket expenditures during the study period. Enrollees in the gatekeeper plan more often identified internists, obstetrician/gynecologists, and specialists as their usual providers of care, while enrollees in the no gatekeeper plan had more often named family physicians (the distribution is similar to source of care before the study, Table 1). Enrollees were more satisfied with the no gatekeeper plan than the gatekeeper plan (very satisfied: 75% - 64% = 11%, 95% CI = 7.63, 14.37).

TABLE 2-Percentage of Enrollees Using Services in the Gatekeeper and No Gatekeeper Plans

Percentage of Enrollees With: Any Services 21 Ambulatory Visit -1 Primary Care Physician Visit .1 Specialist Visit .1 Hospitalization

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Gatekeeper (n = 1419)

No Gatekeeper (n = 1408)

Difference (95% Cl)

74 68 65 23 4.5

77 70 59 32 5.0

-3 (-6.17, +0.17) -2 (-5.41, + 1.41) +6 (+2.43, +9.57) -9 (-12.28, -5.72) -0.5 (-2.07, +1.07)

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GATEKEEPER EFFECT ON HEALTH SERVICES USE, CHARGES TABLE 3-Annual Charges and VlsIts for Enrollees In the Gatekeeper and No Gatekeeper Plans

Total Charges Primary Care Physician Specialist Hospital Charges Primary Care Physician Specialist Ambulatory Charges Primary Care Physician Specialist Ambulatory Visits Primary Care Physician

Specialist

Gatekeeper (n = 1419) Mean

No Gatekeeper (n = 1408) Mean

Difference (95% Cl)

$239 85 155 $ 93 9 84 $146 76 70 2.7 2.1 .63

$254 96 158 $ 87 16 71 $167 80 87 3.0 2.0 .93

-15 (-73.0, +43.0) -11 (-24.4, +2.4) -3 (-52.8, +46.8) +6 (-44.9, +56.9) -7 (-15.4, +1.4) +13 (-32.2, +58.2) -21 (-39.9, -2.1) -4 (-13.2, +5.2) -17 (-30.1, -3.9) -0.3 (-0.60, +0.02) +0.1 (-0.12, +0.32) -0.3 (-0.50, -0.10)

TABLE 4-HospItal Use for Enrollees in the Gatkeeper and No Gatekeeper Plans*

Hospital Admissions per 1000 Person Years Hospital Days per 1000 Person Years Average Length of Hospital Stay Hospital Charges Primary Care Physician Specialist

Gatekeeper Mean

No Gatekeeper Mean

Difference (95% Cl)

49

56

-7 (-25.1, +11.1)

205

277

-72 (-207.8, +63.8)

4.2

$ 196 $1867

4.9

$ 320 $1432

-0.7 (-2.7, +1.3) -124 (-280.4, +32.4) +435 (-378.9, +1248.9)

*The gatekeeper plan had 64 persons with a total of 70 hospitalizations, and the no gatekeeper plan had 70 persons with a total of 79 hospitalizations.

TABLE 5-Charges and Visits for Ambulatory Users In the Gatekeeper and No Gatekeeper Plans

Gatekeeper Per User Per Year

Ambulatory Charges Primary Care Physician

Specialist Ambulatory Visits Prmary Care Physician Specialist

(n = 1052) Mean

$197 102 95 4.0 3.1 .9

Although satisfaction differed, similar percentages of families switched to other plans during the next open enrollment. Discussion In this randomized trial, the gatekeeper plan had lower ambulatory charges per enrollee, primarily due to lower use of specialists. The gatekeeper plan had little impact on hospital use or charges perhaps because of small numbers. The total charges per enrollee were 6 percent lower in the plan with a gatekeeper, a modest difference that was not statistically significant. The gatekeeper plan required patients to see a primary care physician first, so it was not surprising to find that more enrollees in the gatekeeper plan had a visit to a primary care physician. The gatekeeper plan provided no incentives for PCPs to reduce visits to themselves, and indeed PCP visits and charges were similar in the two plans. There were incentives for gatekeepers to limit referrals and this apparently resulted in lower expenditures for specialist services in AJPH December 1989, Vol. 79, No. 12

No Gatekeeper (n = 1087) Mean

$216 104 113 4.3 2.9 1.3

Difference (95% Cl) -19 (-42.4, +4.4) -2 (-13.3, +9.3) -18 (-34.8, -1.2) -0.3 (-0.72, +0.12) +0.2 (-0.08, +0.48) -0.4 (-0.67, -0.09)

the gatekeeper plan. Specialists were offered no incentives by the gatekeeper plan to reduce costs, and once patients were referred to specialists, their volume and charges for various types of procedures were similar in both plans. A gatekeeper effect was seen for certain diagnoses for which treatment is at the discretion of the patient and physician, such as mental health problems and back problems. We do not know if these differences result from: self-selection, decreased initial visits by the enrollee, differences in diagnostic coding, or the practice patterns or specialty of the regular doctor. Future studies of gatekeeper plans should explore utilization by diagnostic category in more detail. True gatekeeper effects are probably at least as large as those reported here. First, the population consisted of subscribers and their family members who chose United Healthcare rather than one of the other state health insurance options available to them. Because the pre-enrollment information described the standard UHC plan, all study participants may 1631

MARTIN, ET AL.

have been oriented to use PCPs more than the general population; therefore, the differences between the plans may be underestimated. Second, differences between plans may have been underestimated because people in the no gatekeeper plan were more likely to have a regular doctor who was already participating in United Healthcare as a gatekeeper. Two other issues should be considered when interpreting these results. First, we could not examine the gatekeeper plan effect in more detail because we were using claims data. We have no indication whether a specific visit was initiated by the patient or provider, or whether the patient was seeing a particular provider as a primary care physician or as a specialist. Furthermore, claims data did not allow us to describe how or to what extent a primary care physician was functioning as a gatekeeper. Second, this 12-month study period may not be representative of the plans' or enrollees' experience over time. One possibility is that individuals in the no gatekeeper plan may have used services differently because they knew that the study period was limited to one year. Another possibility is that the "learning period" for new enrollees may have affected the results. We would expect this learning period to be more important for the gatekeeper plan because enrollees had to adjust to more restrictions on their use of services than in the no gatekeeper plan. Other studies have reported mixed results of the gatekeeper effect on the use of services. Catlin, et al, surveyed use of primary care physicians in staff and group model HMOs and excluded independent practice associations (IPAs).6 They found no significant differences in hospital or ambulatory use among HMOs using more primary care physicians, but the financial incentives offered to primary care physicians were not described. Burkett's descriptive study of an IPA-HMO with gatekeepers and financial incentives similar to UHC found the rate of referral visits to be low.8 In comparing his results to ours, primary care visits per person per year appeared to be slightly higher and use of referral visits even lower than those in this study. The findings of another study of UHC conducted at about the same time provide additional evidence for assessing the gatekeeper concept. In that study, we compared the standard UHC gatekeeper plan with two other health plans: Group Health Cooperative, a staff model HMO with primary care case management; and Blue Cross, which provided fee-for-service hospital and ambulatory care. Use and estimated expenditures were compared across the three plans for a different cohort of Washington State employees which was followed for two years.9 Initial access to care was high at both UHC and Group Health. UHC had lower expenditures for specialists than the other plans, but the savings were not sufficient to decrease overall expenditures. Total annual expenditures per person were similar for UHC and Blue Cross and were significantly higher than expenditures for Group Health. These two studies of United Healthcare, using different study designs, both reported savings on specialist costs in the UHC gatekeeper plan compared to other plans. However, incentives for gatekeepers alone may not be sufficient to contain overall plan costs. In a subsequent case study of United Healthcare, we examined charges for all enrollees from numerous employers in three states. Although United Healthcare may have contained specialist charges, from 1979 to 1982 specialist charges as a percentage of total charges rose, whereas the percentage of charges by gatekeepers fell. 13 After operating for nine years in Washington, California,

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and Utah, United Healthcare was discontinued by SAFECO because of large financial losses, due to management problems and inadequate incentives for specialists and consumers to control costs.'4 The evidence presented in this study suggests that the gatekeeper concept actually may have reduced UHC losses. Hillman describes the conflict of interest that may exist between financial incentives and providing high quality care.2 Whenever utilization decreases, especially for referral care, the question of underutilization of services arises. There is no evidence from our studies or those of others which shows plans with gatekeepers providing higher or lower quality care than other plans. Our study was too small to observe any differences in the overall quality of care. The results of this study are particularly relevant to independent practice associations with incentives similar to United Healthcare. (Since our study population represents employees and their families, these results may not apply to the poor or to retirees.) As the number of gatekeeper plans in the United States continues to grow, the findings of this study have important implications for the design of those plans. First, the United Healthcare incentives for channeling enrollees to primary care physicians increased enrollees' initial use of PCPs and decreased the use of specialists. Second, relatively small financial incentives were sufficient to decrease primary care physician referrals to specialists. It should be emphasized that these incentives applied only to a small proportion of a primarily fee-for-service based practice. Third, the finding of no difference between plans in specialists' use ofprocedures suggests that in the future plans should incorporate incentives for cost control by specialists.

ACKNOWLEDGMENTS

This study was supported by the Health Care Financing Administration, Grant 18-P-9714410.

REFERENCES

1. Eisenberg JM: The internist as gatekeeper: Preparing the general internist for a new role. Ann Intern Med 1985; 102:537-543. 2. Hillman AL: Financial incentives for physicians in HMOs: Is there a conflict of interest? N Engi J Med 1987; 317:1743-1748. 3. Politser P: The gatekeeper concept. ACS Bull 1986; 71:17-20. 4. Paxton HT: Are gatekeepers good for medicine? Med Econ 1986; 63:60-65. 5. Powe NR, Eisenberg JM: Studying and teaching the gatekeeper. J Gen Intern Med 1986; 1:197-198. 6. Catlin RF, Bradbury RC, Catlin RJO: Primary care gatekeepers in HMOs. J Fam Pract 1983; 17:673-678. 7. Phillips RR, Dorsey JL: A look inside: Some aspects of structure and function in forty prepaid group practice HMOs. Group Health J 1980; 1:16-32. 8. Burkett GL: Variations in physicians utilization patterns in a capitation payment IPA-HMO. Med Care 1982; 22:1128-1139. 9. Richardson WC, Martin DP, Diehr P, et al: Consumer choice and cost containment: An evaluation of SAFECO's United Healthcare plan. Vol I of final report to the Health Care Financing Administration, US Department of Health and Human Services. Baltimore, MD: HCFA, 1984. 10. Moore SM: Cost containment through risk-sharing by primary care physicians. N Engl J Med 1979; 300:1359-1362. 11. Duan N, Manning WG, Morris CN, Newhouse JP: A comparison of alternative models for the demand for medical care. Santa Monica: Rand Corp, R-2754-HHS, 1982. 12. Cherkin DC, Rosenblatt RA, Hart LG, et al: The use of medical resources by residency-trained family physicians and general internists: Is there a difference? Med Care 1987; 25:455-469. 13. Moore SH, Martin DP, Richardson WC: Does the primary care gatekeeper control the costs of health care? Lessons from the SAFECO experience. N Engl J Med 1983; 309:1400-1404. 14. Martin DP, Ehreth JL, Geving AR: A Case Study of United Healthcare: Lessons for Other Health Care Plans. Menlo Park, CA: Henry J. Kaiser Family Foundation, 1985.

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