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Objective. To estimate the average survival effects of breast conserving surgery plus irradiation relative to mastectomy for marginal stage II breast cancer patients in Iowa from 1989–1994.
Data Sources/Data Setting. Secondary linked Iowa SEER Cancer Registry—Iowa Hospital Association discharge abstract data for women in Iowa with stage II breast cancer from 1989–1994.
Study Design. Observational instrumental variables (IV) analysis.
Data Collection/Extraction Methods. Women with stage II breast cancer from the Iowa SEER Cancer Registry 1989–1994 who received all of their inpatient care in Iowa were linked with their respective hospital discharge abstracts.
Principal Findings. Breast conserving surgery plus irradiation decreased survival relative to mastectomy for marginal stage II breast cancer patients in Iowa during the early 1990s. In this study marginal patients were those whose surgery choices were affected by differences in area treatment rates and access to radiation facilities.
Conclusions. If marginal patients are representative of patients whose treatment choices would be affected by changes in treatment rates, an increase in the breast conserving surgery plus irradiation rate for stage II early stage breast cancer patients would have decreased survival in Iowa during the early 1990s. Further research with newer data and broader samples is needed to make more current and specific assessments.  相似文献
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The quality and outcomes of care provided by primary care physicians and specialists are increasingly important issues in health policy research. Estimating the effect of specialty care on patient outcomes however is complicated by the observational nature of the studies. Patients treated by specialists are often different in terms of observed and unobserved characteristics that can bias estimates of specialty effects. We illustrate and compare two different analytic approaches, propensity scores and instrumental variables, to infer the causal effect of cardiology care in the ambulatory setting on 18-month mortality among 5467 elderly patients who survived at least 3 months after being hospitalized for a myocardial infarction in New York state during 1994 and 1995. Using both approaches we found reductions in 18-month mortality associated with ambulatory cardiology care. However, reasonable deviations from the assumptions underlying each method led to estimated differences in mortality ranging from a 6% absolute reduction in mortality to a 2% increase among patients who received cardiology care. Choosing an analytic strategy depends on both available data and the policy question of interest. We believe that comparative analyses such as this one, with extensive assessment of the assumptions underlying each method, can provide valuable insights into important policy questions reliant on the analysis of observational data.  相似文献
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In this paper we investigate the causal effect of years of schooling on health and health-related behavior in West Germany. We apply an instrumental variables approach using as natural experiments several changes in compulsory schooling laws between 1949 and 1969. These law changes generate exogenous variation in years of schooling both across states and over time. We find evidence for a strong and significant causal effect of years of schooling on long-term illness for men but not for women. Moreover, we provide somewhat weaker evidence of a causal effect of education on the likelihood of having weight problems for both sexes. On the other hand, we find little evidence for a causal effect of education on smoking behavior. Overall, our estimates suggest significant non-monetary returns to education with respect to health outcomes but not necessarily with respect to health-related behavior.  相似文献
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Byung-Kwang Yoo  MD  PhD    Kevin D. Frick  PhD 《Value in health》2006,9(2):114-122
OBJECTIVE: To assess whether estimates of the effectiveness of influenza vaccination in reducing rates of hospitalizations and all-cause mortality derived from cross-sectional data could be improved by applying the instrumental variable (IV) method to data representing the community-dwelling elderly population in the United States in order to adjust for self-selection bias. METHODS: Secondary data analysis, using the 1996-97 Medicare Current Beneficiary Survey data. First, using single-equation probit regressions this study analyzed influenza-related hospitalization and death due to all causes predicted by vaccination status, which was measured by claims or survey data. Second, to adjust for potential self-selection of the vaccine receipt, for example, higher vaccination rates among high-risk individuals, bivariate probit (BVP) models and two-stage least squares (2SLS) models were employed. The IV was having either arthritis or gout. RESULTS: In single-equation probit models, vaccination appeared to be ineffective or even to increase the probability of adverse outcomes. Based on BVP and 2SLS models, vaccination was demonstrated to be effective in reducing influenza-related hospitalization by at least 31%. The BVP model results implied significant self-selection in the single-equation probit models. CONCLUSIONS: Adjusting for self-selection, BVP analyses yielded vaccine effectiveness estimates for a nationally representative cross-sectional sample of the community-dwelling elderly population that are consistent with previous estimates based on randomized controlled trials, prospective cohort studies, and meta-analyses. This result suggests that analyses with 2SLS and BVP in particular may be useful for the analysis of observational data regarding prevention in which self-selection is an important potential source of bias.  相似文献
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OBJECTIVE: This study investigates the impact of welfare reform on insurance coverage before pregnancy and on first-trimester initiation of prenatal care (PNC) among pregnant women eligible for Medicaid under welfare-related eligibility criteria. DATA SOURCES: We used pooled data from the Pregnancy Risk Assessment Monitoring System for eight states (AL, FL, ME, NY, OK, SC, WA, and WV) from 1996 through 1999. STUDY DESIGN: We estimated a two-part logistic model of insurance coverage before pregnancy and first-trimester PNC initiation. The impact of welfare reform on insurance coverage before pregnancy was measured by marginal effects computed from coefficients of an interaction term for the postreform period and welfare-related eligibility and on PNC initiation by the same interaction term and the coefficients of insurance coverage adjusted for potential simultaneous equation bias. We compared the estimates from this model with results from simple logistic, ordinary least squares, and two-stage least squares models. PRINCIPAL FINDINGS: Welfare reform had a significant negative impact on Medicaid coverage before pregnancy among welfare-related Medicaid eligibles. This drop resulted in a small decline in their first-trimester PNC initiation. Enrollment in Medicaid before pregnancy was independent of the decision to initiate PNC, and estimates of the effect of a reduction in Medicaid coverage before pregnancy on PNC initiation were consistent over the single- and two-stage models. Effects of private coverage were mixed. Welfare reform had no impact on first-trimester PNC beyond that from reduced Medicaid coverage in the pooled regression but separate state-specific regressions suggest additional effects from time and income constraints induced by welfare reform may have occurred in some states. CONCLUSIONS: Welfare reform had significant adverse effects on insurance coverage and first-trimester PNC initiation among our nation's poorest women of childbearing age. Improved outreach and insurance options for these women are needed to meet national health goals.  相似文献
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OBJECTIVE: To compare the estimated effects of dialysis center profit status on patient survival using alternative estimation strategies with retrospective data. DATA SOURCES/STUDY SETTING: Patient and provider-level retrospective data from the United States Renal Data System (USRDS), 1996-1999. STUDY DESIGN: Observational risk adjustment and instrumental variable methods. DATA COLLECTION/EXTRACTION METHODS: Study collected measures from various USRDS files describing clinical characteristics, survival, and the profit status of the initial dialysis center for incident end-stage renal disease (ESRD) patients aged 67+. USRDS facility files were used to assess dialysis center profit status and measure patient distances to dialysis centers. PRINCIPAL FINDINGS: Found survival effect related to profit status in the range of previous research using risk-adjusting covariates similar to those used in previous models. Adding further risk-adjusting covariates halved this effect. The relative proximity of for-profit and nonprofit dialysis centers to the patient residence was the strongest determinant of the profit status of the patient's initial dialysis center. The effect of profit status on survival was eliminated using the two-stage least squares variant of instrumental variable estimation with the relative proximity of for-profit and nonprofit dialysis centers to the patient's residence as the instrument. CONCLUSIONS: Using only the variation in initial dialysis center profit status that was related to the relative proximity of for-profit and nonprofit dialysis centers to the patient, we found no relationship between dialysis center profit status and patient survival. These results are in contrast to results obtained using risk-adjustment methods with a limited set of risk-adjusting covariates.  相似文献
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RESEARCH OBJECTIVE: To estimate the effect of provider advice in routine clinical contacts on patient smoking cessation outcome. DATA SOURCE: The Sample Adult File from the 2001 National Health Interview Survey. We focus on adult patients who were either current smokers or quit during the last 12 months and had some contact with the health care providers or facilities they most often went to for acute or preventive care. STUDY DESIGN: We estimate a joint model of self-reported smoking cessation and ever receiving advice to quit during medical visits in the past 12 months. Because providers are more likely to advise heavier smokers and/or patients already diagnosed with smoking-related conditions, we use provider advice for diet/nutrition and for physical activity reported by the same patient as instrumental variables for smoking cessation advice to mitigate the selection bias. We conduct additional analyses to examine the robustness of our estimate against the various scenarios by which the exclusion restriction of the instrumental variables may fail. PRINCIPAL FINDINGS: Provider advice doubles the chances of success in (self-reported) smoking cessation by their patients. The probability of quitting by the end of the 12-month reference period increased from 6.9 to 14.7 percent, an effect that is of both statistical (p < .001) and clinical significance. CONCLUSIONS: Provider advice delivered in routine practice settings has a substantial effect on the success rate of smoking cessation among smoking patients. Providing advice consistently to all smoking patients, compared with routine care, is more effective than doubling the federal excise tax and, in the longer run, likely to outperform some of the other tobacco control policies such as banning smoking in private workplaces.  相似文献
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OBJECTIVE: To propose and test a method that produces an unbiased estimate of the average effect of smoking cessation on weight gain. Previous estimates may be biased due to unobservable differences in attributes of quitters and continuing smokers. An accurate estimate of weight gain due to cessation is important for policymakers, health managers, clinicians, consumers, and developers of smoking cessation aids. STUDY SETTING: Our analysis consisted of an instrumental variables (IVs) approach in which treatment assignment in randomized smoking cessation trials served as a random source of variation in probability of quitting. DATA COLLECTION: We searched the medical literature for previously conducted smoking cessation trials that contained data suitable for our reanalysis. PRINCIPAL FINDINGS: We identified one trial for our reanalysis, the Lung Health Study, a randomized smoking cessation trial with 5,887 smokers aged 35-60 from 1986 to 1994 in several sites across the United States. In our IV reanalysis, we estimated a 9.7 kg weight gain over 5 years due to cessation, as compared with the conventional estimate of 5.3 kg. CONCLUSIONS: The true effect of smoking cessation on weight gain may be larger than previously estimated. This result indicates the importance of fully understanding the possible weight effects of cessation and underscores the need to accompany cessation programs with weight management interventions. The result, however, does not overturn the conclusion that the net health benefits of quitting are positive and very large. The application of the IV technique we propose is likely to be useful in a variety of contexts in which one is interested in the effect of one health condition on another.  相似文献
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