Affiliations of authors: Department of Health Care Policy (NLK, MBL, EM, EG), Harvard Medical School; the Division of General Internal Medicine, Brigham and Women's Hospital, Boston, MA (NLK); the Schools of Medicine and Public Health, and Jonsson Cancer Center, University of California, Los Angeles, CA (PAG)
Correspondence to: Nancy L. Keating, MD, MPH, Department of Health Care Policy, Harvard Medical School, Boston, MA 02115 (e-mail: keating{at}hcp.med.harvard.edu).
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ABSTRACT |
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INTRODUCTION |
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The President's 20002001 Cancer Panel identified the potential for a negative impact from the expansion of managed care on quality of care (7), and the National Cancer Policy Board's report Ensuring Quality Cancer Care called for large, carefully designed studies to assess how features of managed care plans and market areas affect the quality of cancer care (8). To date, few empirical studies have assessed the impact of increases in the market share of managed care on quality of care and the few that are available have examined primarily cardiovascular disease. These studies have demonstrated a positive association between the market share of managed care and the use of aspirin and beta-blockers after myocardial infarction (4) but a small negative association with necessary coronary angiography (4,9). Whether the market share of managed care influences the quality of cancer care is unknown. Recent Medicare legislation (10) and increases in Medicare payments to health maintenance organizations (HMOs) (11) are likely to expand the enrollment of Medicare beneficiaries in managed care plans, heightening the need to understand the potential consequences of increases in managed care market share on the quality of care for all Medicare beneficiaries.
There are several potential mechanisms by which increases in the market share of managed care might negatively influence the quality of cancer care. First, managed care may affect the composition of provider specialty in a market, resulting in fewer cancer specialists, i.e., those providers who may be the best trained to provide high-quality cancer care. Second, the expansion of managed care in a market may influence the availability of technology. For example, there is some evidence that areas with a high managed care market share have fewer magnetic resonance imaging facilities and fewer mammography providers than areas with a low managed care market share (12,13). Third, greater managed care activity may lead to difficulties in accessing care, regardless of patients' insurance status (14), and decreased access to care could lead to the receipt of lower quality care.
Alternatively, increases in managed care market share may positively influence the quality of cancer care if managed care has improved the ability of providers and health care organizations to deliver effective, evidence-based care more efficiently (for example, through the use of information systems, feedback to providers, and treatment guidelines). Finally, the effect of managed care on the quality of cancer care might vary by the type of indicator measured, as noted for patients with acute myocardial infarction, with increases in managed care market share associated with greater use of appropriate medications (4) but slightly lower rates of more costly invasive procedures (4,9,15).
In this study, we used longitudinal data to assess whether increases in the market share of managed care were associated with the quality of cancer care for Medicare patients treated in the fee-for-service sector. We studied patients with breast cancer and colorectal cancer, two prevalent cancers for which several quality-of-care indicators have been developed.
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METHODS |
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We used Surveillance, Epidemiology, and End Results (SEER1)Medicare data for this analysis (16). The SEER program of the National Cancer Institute collects uniformly reported data from 11 population-based cancer registries covering approximately 14% of the United States population (17). For each incident of cancer, the SEER registries collect information on month and year of diagnosis, cancer site, histologic type, American Joint Committee on Cancer stage (18), and patient demographic characteristics, including county of residence. The registries also collect information on surgical and radiation treatments administered or planned in the 4 months after diagnosis.
Since 1991, the SEER data have been merged with Medicare administrative data by a matching algorithm that has successfully linked files for more than 94% of SEER registry patients diagnosed at age 65 years or older (16). The Medicare claims data used in this study included the Medicare Provider Analysis and Review file (inpatient claims), the 100% Physician/Supplier file (claims for physicians' services and other medical services), and the Hospital Outpatient Standard Analytic file (claims for outpatient facility services). The study was approved by the Harvard Medical School Committee on Human Studies and the Institutional Review Board of the University of California at Los Angeles.
Study Cohorts
We selected patients with a first diagnosis of invasive breast cancer or colorectal cancer from 1993 through 1999 who were at least 66 years old at the time of their cancer diagnosis and who were continually enrolled in fee-for-service Medicare Parts A and B from 1 year before diagnosis through diagnosis (N = 48 149 women with breast cancer and 54 744 men and women with colorectal cancer). We excluded patients whose tumor histology indicated a primary cancer other than that of interest, patients whose diagnosis was reported only by autopsy or death certificate, and patients whose month of diagnosis was unknown. We also excluded patients who were enrolled in a HMO at any time during the year before diagnosis because claims for these patients are not routinely submitted, and we excluded patients with no claims from 45 days before diagnosis through 195 days after diagnosis because we considered their claims incomplete. Finally, we excluded patients with cancers of unknown stage. The final sample size included 41 394 patients with breast cancer and 48 027 patients with colorectal cancer who were potentially eligible for analyses. Additional inclusion criteria for specific quality indicators are included in Table 1.
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To measure quality of care, we selected quality indicators that have been recommended by various groups (Table 1). For breast cancer, we examined whether women with early-stage breast cancer underwent mammography during months 7 through 18 after diagnosis [annual mammography is recommended for such patients (1921); our data and that of others (22) suggests a peak in mammography 12 months after diagnosis]. We also examined whether patients had annual mammography over a 2-year period after diagnosis, i.e., during months 7 through 18 and months 19 through 30. Finally, we assessed whether women who underwent breast-conserving surgery received radiation therapy (23,24).
For colorectal cancer, we examined whether patients with stage III colon cancer received adjuvant chemotherapy and whether patients with stage II or III rectal cancer received adjuvant chemotherapy and adjuvant radiation therapy (25,26). We also assessed whether patients with stage I, II, or III colorectal cancer had a full colonoscopy pre- or perioperatively. In addition, we examined two surveillance tests: receipt of two carcinoembryonic antigen (CEA) tests within 14 months of surgery for patients with stage II or III colorectal cancer (recommended every 3 months) and receipt of colonoscopy during months 7 through 18 after diagnosis for patients with stage I, II, and III colorectal cancer (21,2732). Additional inclusion criteria were applied to select the cohorts eligible for each of the quality indicators, as indicated in Table 1.
Managed Care Market Share
We measured the market share of managed care for each of the 202 counties represented in our sample. We defined managed care market share as the number of Medicare beneficiaries enrolled in all managed care contract plans in a county divided by the number of Medicare-entitled beneficiaries in that county, and we calculated market share for each year using data for 19921999 obtained from the Centers for Medicare and Medicaid Services (CMS). We defined the market share of managed care based on Medicare beneficiaries because it represents managed care activity with the most direct link to Medicare beneficiaries, who were the focus of our study. Although managed care activity outside of Medicare might also influence quality of care for Medicare beneficiaries in the fee-for-service sector, overall market share of managed care is not directly available at the county level for our period of study. Nevertheless, Baker (2) reported that the Medicare managed care market share is highly correlated with managed care market share overall.
We categorized managed care market share for each patient (based on the market share in the county where they lived in the year during which they were diagnosed) as <1%, 1%10%, >10%30%, and >30%. These categories reflect the approximate quartiles for the patients in the sample over the study period. Similar cut points have been used previously (1214). Our modeling strategy, described below, allowed us to estimate expected changes in the proportion of patients receiving each quality indicator if the patients were similar with regard to demographic and clinical characteristics and living in the same county and if the market share of managed care in that county changed from one category to another, with everything else being equal.
Control Variables
We obtained information about age, race, Hispanic ethnicity, marital status, year of diagnosis, tumor stage, tumor grade, tumor size, and history of previous cancer from the SEER registry data. We categorized these variables as shown in Table 2. We used 1990 U.S. Census data to obtain information on education level and annual income by the census tract of residence; patients were assigned to quartiles within each registry to account for regional differences in income and educational level. To measure comorbid illnesses, we calculated diagnostic cost groups (33), a risk adjustment tool used by the CMS to predict disease burden and future costs for Medicare beneficiaries by using diagnostic information from both inpatient and ambulatory claims. This tool captures many more diagnoses than does the Charlson score (34), and this tool has been shown to predict mortality after admission for myocardial infarction more accurately among Medicare beneficiaries than does the Charlson score (35). We used the Medicare all-encounter model, Release 6.1, to calculate diagnostic cost groups based on the 12-month period that began 14 months before the diagnosis of cancer to best characterize patients' comorbid diseases before diagnosis, and we then categorized the scores in quartiles.
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We estimated logistic regression models to assess the effect of increases in the market share of managed care on quality for each binary indicator among the relevant patient cohorts described in Table 1. For each model, the patient was the unit of analysis, which allowed for adjustment for the various individual level covariates (described above) that were included in the models. We also included county of residence in all models, allowing these fixed effects to account for time-invariant differences across counties that could be associated with both the market share of managed care penetration and the dependent variables (36), including factors such as baseline differences in managed care market share by county. For each model, the independent variables of interest were the binary variables designating the category of managed care market share for the patient in the county of residence at the time of their diagnosis. In all models, we adjusted standard errors for clustering of outcomes within registry. Patients living in counties for which there was no variation in the dependent variable of interest were not included in the relevant analysis.
To aid in interpretation of the results for each model, we used the coefficients on the categorical managed care market share variable to calculate the adjusted proportion of patients in each of the four categories of managed care market share who received the quality indicator of interest. Next, we calculated the percentage point change, or difference, in the outcome of interest resulting from increases in the market share of managed care from <1% to each of the other categories. Because our data were longitudinal and each model included a fixed county effect, these differences effectively estimated the impact of changes in the market share of managed care within counties, everything else being constant. For example, if the market share of managed care in the county were to change from one category to another, then these percentage point changes would reflect the difference in the probability of receiving the quality indicator for two patients with identical characteristics living in the same county. By assigning patients to one of four different categories of managed care market share rather than using a single continuous variable, the models also allow for effects that differ with the baseline rate of managed care market share in a county.
For some indicators, the market share of managed care in the county during the year before diagnosis may be more relevant than that during the year of diagnosis (particularly for patients diagnosed early in a given year). Therefore, we conducted a sensitivity analysis in which we repeated all multivariable models assigning managed care market share based on the year before diagnosis. In a second sensitivity analysis, we repeated all multivariable models after excluding the registry that was comprised of a single county (Los Angeles County).
Descriptive analyses were conducted using SAS statistical software, version 8.2 (SAS Institute, Cary, NC). Multivariable analyses were conducted using Stata software, version 8 (StataCorp LP, College Station, TX). P values were two-sided. We did not adjust P values for multiple comparisons because approaches to do so assume independence of the dependent variables and would therefore be overly conservative, understating the statistical significance of the findings.
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RESULTS |
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The market share of managed care varied substantially by county. Some counties had little variation in managed care market share over time, particularly the Los Angeles County registry (i.e., one county in one registry with a high level of managed care market share) and the Iowa registries (i.e., 99 counties with the lowest level of managed care market share). However, there was a good deal of variation in managed care market share over time in the other registries. Table 3 illustrates registry level changes in managed care market share over time by providing levels of managed care market share at the beginning and at the end of the study. Consistent with patterns of Medicare managed care enrollment, we observed increases in the market share of managed care in most counties until the late 1990s when it decreased, presumably because many plans that had been participating in Medicare managed care withdrew from the program after the formula for payments was revised as part of the Balanced Budget Act of 1997 (37).
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The proportion of Medicare beneficiaries enrolled in managed care was not associated with changes in receipt of surveillance mammography after diagnosis for women in the fee-for-service sector (P = .83 for mammography 1 year after diagnosis and P = .68 for annual mammography during the first 2 years after diagnosis) or with receipt of radiation after breast-conserving surgery among women who underwent breast-conserving surgery (P = .16) (Table 4).
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The managed care market share also had mixed associations with quality indicators relating to procedures and testing. Managed care market share was not associated with complete pre- or perioperative colonoscopy (P = .27) or with surveillance colonoscopy (P = .39) during months 7 through 18 after diagnosis for patients with stage I, II, or III colorectal cancer. However, managed care market share was associated with receipt of at least two CEA tests within 14 months after surgery among patients with stage II or III colorectal cancer (P = .001); patients in areas in which the managed care market share increased to >30% were more likely than other patients to receive CEA tests (Table 4).
In sensitivity analyses, we repeated all multivariable models assigning managed care market share based on the year before diagnosis. Results were generally similar to those described above. In the second sensitivity analysis, we repeated analyses excluding the Los Angeles County registry that made up a single county; again, the results were similar.
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DISCUSSION |
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Although performance on most indicators of quality was relatively poor overall, our study found no association between increases in managed care market share and quality of care for most indicators examined. Our observed rates were consistent with those reported in other studies (38,39), suggesting that substantial improvements in quality remain possible.
We did observe two indicators that varied according to a change in the market share of managed care. The rates of adjuvant chemotherapy and radiation therapy among patients with stage II or III rectal cancer peaked in areas where the market share of managed care increased or decreased to 1%10%. This change may reflect better systems of care for providers in counties with moderate increases in managed care penetration but an inability to maintain the provision of expensive services, such as adjuvant chemotherapy and radiation therapy, in areas with further increases in the market share of managed care. Nevertheless, the difference in rates of adjuvant therapy for patients with stage II and III rectal cancer were small and overall rates were low, suggesting substantial room for improvement in care for all patients.
We observed increased rates of postoperative CEA testing only as the managed care market share in an area increased from the lower levels to the >30% category. Many guidelines put forth during the early 1990s did not make recommendations about CEA testing for surveillance testing; not until the later half of the decade was this test recommended more consistently (22,2729,40,41). Providers practicing in areas with the largest increases in the market share of managed care may have been best able to adopt and implement this surveillance recommendation.
Our study has several limitations. First, we studied elderly patients living in regions of the country with SEER registries. Although the elderly population residing in the SEER areas is similar to the general U.S. population in terms of age and sex, the SEER population has a higher proportion of nonwhite persons, is more likely to live in urban areas, and is enrolled in Medicare HMOs more often than the general U.S. population (42,43). Nevertheless, this population-based sample includes cancer patients from areas representing 14% of the U.S. population (42,43). In addition, the number of counties per registry varied from 1 (the Los Angeles registry) to 99 (the Iowa registries). However, our findings were robust to the exclusion of patients from the Los Angeles registry, indicating that our results were not driven by one large registry.
Second, we studied care for elderly patients with two types of cancer only. However, elderly patients account for approximately two-thirds of patients with cancer, and the cancers we studied are two of the most commonly diagnosed cancers (44). Third, although the use of longitudinal data is a major strength of our study because it allows us to account for time-invariant unobserved effects, such longitudinal data are subject to dynamic selection effects. For example, if managed care organizations are more likely to enroll relatively younger and healthierpatients, then, as the managed care market share increases, the health status of patients in the fee-for-service sector in that area may become relatively worse. If patients with more comorbid illnesses met fewer quality standards, one could conclude, incorrectly, that increases in managed care were associated with worse quality. However, because we saw modest changes in quality of care associated with increased managed care market share, this particular dynamic selection effect does not seem to explain our findings. Fourth, we did not adjust the P values for multiple comparisons because most adjustment methods would be overly conservative. Nevertheless, our general conclusion that the market share of managed care has a limited effect on quality in the fee-for-service sector would not change, even if the levels of statistical significance of our findings had been overstated.
Finally, we lacked information about the specific managed care products in the markets we studied (i.e., group/staff model HMOs, Independent Practice Association (IPA)/network HMOs, and preferred provider organizations [PPOs]). Spillover effects may be more prominent in areas with more PPOs and IPAs and fewer group/staff model HMOs because physicians who practice in IPAs and PPOs typically care for patients enrolled in managed care plans and for patients enrolled in fee-for-service plans, and therefore, it becomes increasingly likely that their practice style may be similar for both groups of patients. Despite trends in managed care overall during the 1990s toward PPOs and IPA-model HMOs, suggesting that much of the managed care activities in the areas we studied were such products, we still saw minimal spillover effects. Moreover, although differential benefit structures offered by HMOs in an area may influence benefits offered by fee-for-service products in the same area, all patients included in our study were enrolled in fee-for-service Medicare and had the same benefits.
In this population-based sample of elderly patients diagnosed with breast or colorectal cancer, increases in managed care market share had limited or no effect on the quality of care delivered. Fears that spillover effects from increases in managed care would have large negative effects on the quality of cancer care for patients not in managed care appear to be unfounded. However, hopes that expansion of managed care may improve quality for all patients by promoting the efficient delivery of effective, evidence-based care have also not been realized.
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NOTES |
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This study used the linked SEER-Medicare database. The interpretation and reporting of these data are the sole responsibility of the authors. We acknowledge the efforts of the Applied Research Program, NCI; the Office of Research, Development and Information, CMS; Information Management Services, Inc.; and the SEER Program tumor registries in the creation of the SEER-Medicare database.
This work was funded by grant CA 0092588 from the NCI. Dr. Keating's effort was also funded in part by a Clinical Scientist Development Award from the Doris Duke Charitable Foundation.
We thank Yang Xu, MS, for expert programming assistance.
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Manuscript received August 16, 2004; revised November 10, 2004; accepted December 13, 2004.
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