Discussion
The audit methodology we used in this study measured the delivery of adult clinical preventive services in a multispecialty, multisite group practice health system that treats both FFS and HMO patients. The audited group included all patients having at least one face-to-face encounter with a primary care provider in 1995. This methodology excluded patients who were not seen during the audited year. Peripheral sites where billable services were not recorded were also excluded. Positive audit criteria were determined according to nationally recognized norms.25
Limitations
Two random medical record reviews validated the computerized billing file audit showing that most recorded preventive procedures were performed for screening, and few patients had received any preventive services elsewhere. (The exceptions were the approximately 33% of sigmoidoscopies that were done for symptoms and a small percentage of Papanicolaou tests that were performed outside the system.) The magnitude of these discrepancies was insufficient to alter the conclusions of our study. It is possible that physicians did not code for some preventive visits scheduled by FFS patients whose insurance did not cover prevention. If so, our audit could have underestimated the association of scheduling preventive visits with the delivery of such services for FFS patients. There was no incentive for physicians to undercode preventive visits for HMO patients. The system of care did not record assignment of patients to individual physicians. Therefore, it was not possible to audit individual providers. The system’s database did not record demographic information, such as education, income, ethnic origin, or race. Thus, we could not analyze health system performance in regard to socioeconomic status, which is an important additional predictor of preventive service use.26 Nonbillable services, such as smoking cessation counseling and blood pressure testing, were not measurable using our methodology.
FFS Versus HMO Insurance
With one exception,27 studies of HMO and FFS care have compared one group treating HMO patients with another group providing care for FFS patients. That type of study design raises the concern that system factors (different provider group attitudes, training, system access, protocols, and so forth) were responsible for the differences reported between HMO and FFS care. It is unlikely that this happened in our study, because both HMO and FFS patients were seen within the same system of care by the same physicians whose compensation formula did not discriminate between insurance types. In this system of care, HMO members had insurance to pay for any preventive service offered by the physician, while coverage for prevention was not uniformly available to FFS policy holders.
Our results that show HMO patients received more preventive services than FFS patients agree with the results of the National Health Interview Survey (NHIS),11 which included a representative sample of the US population. It is unlikely that HMO self-selection accounted for the higher preventive services delivery rates for HMO patients in these studies. After controlling for factors correlated with selection into HMOs, health status, and use of medical services, results of the NHIS were not altered. In our study, only half of the HMO patients scheduled a preventive visit; the other half had lower screening rates Table 4.
The most important determinant of access to health care is having health insurance.28 We believe the most simple explanation for the superiority of preventive service delivery to HMO patients in our system of care is that FFS patients without preventive coverage are reluctant to pay out-of-pocket expenses for these services. This belief is supported by the results of a recent study in managed care settings showing that physician compensation method was not significantly related to use, while plan benefit level was positively related to increased service delivery.9 Thus, providing insurance coverage to pay for preventive care is one potential strategy for increasing delivery.
Preventive Visits Versus Acute Care
Visit frequency has previously been shown to have a positive association with the delivery of preventive services.4,29 Our study confirms the association with visit frequency, but found a statistically independent and greater association with visit type. Similar to results in other primary care studies,30 we found that a scheduled preventive visit was strongly predictive of the delivery of preventive services.
One strategy, then, for rectifying this discrepancy is to insist that all patients schedule a yearly preventive visit. Currently only one third of patients in primary care settings31 schedule such a visit. A simple calculation demonstrates, however, that if primary physicians in our audit spent 30 additional minutes each year performing a complete physical examination for the approximately 54,000 patients currently seen for acute care only, there would be little or no time remaining to care for sick patients. Since the audited group represents only a part of the whole, the systemwide impact would be even greater. Additionally, when one author (D.L.H.) systematically invited all adults aged older than 50 years to schedule a complete physical examination, most did not do so (unpublished observations).