The effect of area HMO market share on cancer screening

Health Services Research, Dec, 2004 by Laurence C. Baker, Kathryn A. Phillips, Jennifer S. Haas, Su-Ying Liang, Dean Sonneborn

In addition to influencing the care provided to the patients they cover, the activities of HMOs and other managed care organizations may also bring about changes in the structure and functioning of the health care system with broader implications for health care delivery. Such "spillover effects" of managed care could ultimately affect all of the health care delivered in the United States, including health care for patients who have not joined managed care organizations.

Existing literature suggests that managed care can influence treatment patterns for non-managed care patients. Prior work suggests that increases in HMO market share are associated with declines in expenditures for the care of patients covered by traditional, fee-for-service, Medicare (Baker 1999; Baker and Sharkarkumar 1998). Other studies indicate that areas with high levels of HMO activity have lower total hospital costs (Gaskin and Hadley 1997; Robinson 1991; Robinson 1996; Noether 1988) and that HMO activity affects premiums for non-HMO health insurance (Baker and Corts 1996; Feldstein and Wickizer 1995; Frank and Welch 1985; Baker et al. 9000). Some work suggests that increases in the number of Medicare beneficiaries enrolled in Medicare HMOs are associated with lower overall Medicare expenditures (Welch 1994; Baker 1997; Clement, Gleason, and Brown 1992; Rodgers and Smith 1995).

All of these studies focused on measures related to spending. While differences in spending suggest differences in treatment patterns, relatively little work directly examines treatment patterns. Nonetheless, understanding the extent to which managed care activity is associated via spillover effects with treatment patterns, and the ways in which treatment patterns are affected, is necessary for the formation of a clear understanding of the overall impact of managed care on health care delivery and for the formation of optimal policy responses to changes in the size and characteristics of managed care plans.

This article examines the relationship between area managed care activity and the use of appropriate cancer screening. We use Medical Expenditure Panel Survey (MEPS) data to identify, the timely receipt of screening for breast, cervical, and prostate cancer among patients for whom such screening is appropriate. Screening for cancer is an area in which it is quite plausible that managed care could influence treatment patterns. Studies of managed care and cancer screening (primarily mammography) have generally found that screening is higher among patients enrolled in HMOs or other managed care plans than patients in less-managed types of plans, although more recent studies examining a wider range of plan types have had ambiguous results (Tu, Kemper, and Wong 1999; Gordon, Rundall, and Parker 1998; Solanki and Schauffler 1999; Bernstein, Thompson, and Harlan 1991; Potosky et al. 1998; Phillips et al. 1998; Brown et al. 1990; Zapka et al. 1991; Hsia et al. 2000; Wee et al. 2001; Tye, Phillips, and Liang 2004; Phillips et al. 2004). These studies suggest the potential for area-level managed care to influence screening, but little work examines this issue specifically (Phillips 1998). Work on cancer diagnosis and treatment rates (Baker and McClellan 2001) and work on mammography facilities (Baker and Brown 1999) also suggests the potential for an effect of area-level managed care, but does not directly examine screening.

POTENTIAL MECHANISMS AND EMPIRICAL APPROACH

By "spillover effects," we mean effects of the area level of managed care activity on non-managed care patients. There are a number of potential mechanisms by which spillover effects could come about. We believe two types of mechanisms are particularly applicable to a discussion of screening. First, spillover effects could come about through changes in physician practice patterns. For example, suppose that the care management, information dissemination, and other practices of HMOs lead to changes in the practice styles of HMO doctors (at least when treating HMO patients) that produce higher screening rates among HMO patients. Such a "better" practice style could spread to other providers. If there are physicians who treat primarily non-HMO patients, then as the number of HMO patients increases (and thus as the number of HMO doctors in their area increases), non-HMO doctors may come in contact with HMO doctors more frequently, and information about practice style may be transferred to the non-HMO doctors who may, in turn, adopt techniques that increase their screening rate. In a similar way, doctors who treat both HMO and non-HMO patients may find that their practice style is shifted more and more toward the "HMO" way of doing things as the share of their patients from HMOs rises. Physicians increasingly conditioned to function in a managed care environment may find themselves treating even fee-for-service patients with more of a managed care mindset.

A related possibility is that there are effects at the patient level. Non-managed care patients in markets with high levels of activity by plans that endeavor to increase screening rates may more frequently encounter managed care plan materials, other individuals who have been screened, or other forms of encouragement that promote screening. This may then influence their behavior.