Wei Zhang

Harvard Medical School, Boston, MA, United States

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Publications (3)18.14 Total impact

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    ABSTRACT: To profile hospitals by survival rates of colorectal cancer patients in multiple periods after initial treatment. California Cancer Registry data from 50,544 patients receiving primary surgery with curative intent for stage I-III colorectal cancer in 1994-1998, supplemented with hospital discharge abstracts. We estimated a single Bayesian hierarchical model to quantify associations of survival to 30 days, 30 days to 1 year, and 1-5 years by hospital, adjusted for patient age, sex, race, stage, tumor site, and comorbidities. We compared two profiling methods for 30-day survival and four longer-term profiling methods by the fractions of hospitals with demonstrably superior survival profiles and of hospital pairs whose relative standings could be established confidently. Interperiod correlation coefficients of the random effects are (95 percent credible interval 0.27, 0.85), (0.20, 0.76), and (0.19, 0.82). The three-period model ranks 5.4 percent of pairwise comparisons by 30-day survival with at least 95 percent confidence, versus 3.3 percent of pairs using a single-period model, and 15-20 percent by weighted multiperiod methods. The quality of care for colorectal cancer provided by a hospital system is somewhat consistent across the immediate postoperative and long-term follow-up periods. Combining mortality profiles across longer periods may improve the statistical reliability of outcome comparisons.
    Health Services Research 06/2011; 46(3):729-46. · 2.49 Impact Factor
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    ABSTRACT: To assess associations of patient characteristics with quality-related characteristics of the hospitals where they were treated for colorectal cancer and the role of these associations in disparities in treatment quality affecting vulnerable patient groups or variations across health plans. Population-based cancer registry in California. A total of 38 237 patients diagnosed with stage I-III (non-metastatic) colorectal cancer in California between 1994 and 1998. Registry data were linked with hospital discharge abstracts, US census data, and Medicare enrollment data. The associations of patients' sociodemographic, clinical, and geographic covariates with treatment at high-volume institutions were assessed with logistic regression. The associations of patients' covariates with the risk-adjusted 30-day mortality rates of the hospitals where they received surgery were tested with linear regression. Patients with more advanced tumor stage or more extensive comorbidity, those of Hispanic or Asian race/ethnicity, and those from less affluent communities were less likely to undergo surgery at high-volume institutions and were treated at hospitals with higher risk-adjusted 30-day postoperative mortality rates than those who were less severely ill, white, or more affluent, respectively (all P < 0.05). Black patients also received surgery at hospitals with above-average mortality. Among patients 65 years and older, Medicare managed-care enrollees underwent surgery in higher-volume hospitals than Medicare fee-for-service enrollees, and there was substantial variation in hospital volume and adjusted hospital mortality among Medicare managed-care plans. Improving access of sicker, poorer, and minority patients to high-quality hospitals for cancer surgery may improve their outcomes. Further study of processes affecting hospital referral is warranted.
    International Journal for Quality in Health Care 03/2007; 19(1):11-20. · 1.58 Impact Factor
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    ABSTRACT: Postoperative mortality after some types of cancer surgery is inversely related to the number of operations performed at a hospital (i.e., hospital volume). This study assessed the association of hospital volume with colostomy rates and survival for patients with rectal cancer in a large representative cohort identified from the California Cancer Registry. We identified 7257 patients diagnosed from January 1, 1994, through December 31, 1997, with stage I-III rectal cancer who underwent surgical resection. Registry data were linked to hospital discharge abstracts and ZIP-code-level data from the 1990 U.S. Census. Associations of hospital volume with permanent colostomy and 30-day mortality were assessed with the Mantel-Haenszel trend test and logistic regression. Overall survival was examined with the Kaplan-Meier method and a multivariable Cox proportional hazards model. Multivariable analyses adjusted for demographic and clinical variables and patient clustering within hospitals. All tests of statistical significance were two-sided. In unadjusted analyses across decreasing quartiles of hospital volume, we observed statistically significant increases in colostomy rates (29.5%, 31.8%, 35.2%, and 36.6%; P<.001) and in 30-day postoperative mortality (1.6%, 1.6%, 2.9%, and 4.8%; P<.001) and a decrease in 2-year survival (83.7%, 83.2%, 80.9%, and 76.6%; P<.001). The adjusted risks of permanent colostomy (odds ratio [OR] = 1.37, 95% confidence interval [CI] = 1.10 to 1.70), 30-day mortality (OR = 2.64, 95% CI = 1.41 to 4.93), and 2-year mortality (hazard ratio = 1.28, 95% CI = 1.15 to 1.44) were greater for patients at hospitals in the lowest volume quartile than for patients at hospitals in the highest volume quartile. Stratification by tumor stage and comorbidity index did not appreciably affect the results. Adjusted colostomy rates varied statistically significantly (P<.001) among individual hospitals independent of volume. Rectal cancer patients who underwent surgery at high-volume hospitals were less likely to have a permanent colostomy and had better survival rates than those treated in low-volume hospitals. Identifying processes of care that contribute to these differences may improve patients' outcomes in all hospitals.
    CancerSpectrum Knowledge Environment 06/2003; 95(10):708-16. · 14.07 Impact Factor