Optimal matching with minimal deviation from fine balance in a study of obesity and surgical outcomes

How well can fine balance work for covariate balancing

Fine balance is a matching technique to improve covariate balance in observational studies. It constrains a match to have identical distributions for some covariates without restricting who is matched to whom. However, despite its wide application and excellent performance in practice, there is very little theory indicating when the method is likely to succeed or fail and to what extent it can remove covariate imbalance. In order to answer these questions, this paper studies the limits of what is possible for covariate balancing using fine balance and near-fine balance. The investigations suggest that given the distributions of the treated and control groups, in large samples, the maximum achievable balance by using fine balance only depends on the matching ratio (ie, the ratio of the sample size of the control group to that of the treated group). In addition, the results indicate how to estimate this matching ratio threshold without knowledge of the true distributions in finite samples. The findings are also illustrated by numerical studies in this paper.

Comparison of real-world clinical and economic outcomes in patients receiving oral anticoagulants: A retrospective claims analysis

BACKGROUND: Direct oral anticoagulants (DOACs) have become widely used for the prevention of stroke in nonvalvular atrial fibrillation (AF) and for the treatment of venous thromboembolism (VTE). Warfarin, the standard of care prior to DOACs, requires monitoring and dose adjustment to ensure patients remain appropriately anticoagulated. DOACs do not require monitoring but are significantly more expensive. We sought to examine real-world effectiveness and costs of DOACs and warfarin in patients with AF and VTE. OBJECTIVE: To examine clinical and economic outcomes. The clinical objectives were to determine the bleeding and thrombotic event rates associated with DOACs vs warfarin. The economic objectives were to determine the cost associated with these events, as well as the all-cause medical and pharmacy costs associated with DOACs vs warfarin. METHODS: This analysis was an observational, propensity-matched comparison of retrospective medical and pharmacy claims data for members enrolled in an integrated health plan between October 1, 2015, and September 30, 2020. Members who were older than 18 years of age with at least 1 30-day supply of warfarin or a DOAC filled within 30 days of a new diagnosis of VTE or nonvalvular AF were eligible for the analysis. Cox hazard ratios were used to compare differences in clinical outcomes, where paired t-tests were used to evaluate economic outcomes. RESULTS: After matching, there were 893 patients in each group. Among matched members, warfarin was associated with increased risk of nonmajor bleeds relative to apixaban (hazard ratio [HR] = 1.526; P = 0.0048) and increased risk of pulmonary embolism relative to both DOACs (apixaban: HR = 1.941 [P = 0.0328]; rivaroxaban: HR = 1.833 [P = 0.0489]). No statistically significant difference was observed in hospitalizations or in length of stay between warfarin and either DOAC. The difference-in-difference (DID) in total costs of care per member per month for apixaban and rivaroxaban relative to warfarin were $801.64 (P = 0.0178) and $534.23 (P = 0.0998) more, respectively. DID in VTE-related cost for apixaban was $177.09 less, relative to warfarin (P = 0.0098). DID in all-cause pharmacy costs for apixaban and rivaroxaban relative to warfarin were $342.47 (P < 0.0001) and $386.42 (P < 0.001) more, respectively. CONCLUSIONS: Warfarin use was associated with a significant decrease in total cost of care despite a significant increase in VTE-related costs vs apixaban. Warfarin was also associated with a significant increase in other nonmajor bleeds relative to apixaban, as well as a significant increase in pulmonary embolism relative to both DOACs. Warfarin was associated with a significant reduction in all-cause pharmacy cost compared with either DOAC. DISCLOSURES: The authors of this study have nothing to disclose.

Evaluating and improving a matched comparison of antidepressants and bone density

Matching is a common approach to covariate adjustment in estimating causal effects in observational studies. It is important to assess covariate balance of the matched samples. This is usually done informally, in ways that have a number of limitations. First, there are many diagnostics, even if covariates are assessed one at a time, which raises multiplicity issues. In addition, joint distributions of covariates, even bivariate distributions, are often ignored. Further, it is an open question whether diagnostics identify the major problems. To address these issues, a formal assessment of covariate balance is developed in the current paper. Unlike the common informal diagnostics, the proposed method compares both marginal distributions and joint distributions of the matched sample with those of the benchmark, complete randomizations. The method controls the probability of falsely identifying a covariate imbalance among many comparisons, yet it has a high probability of correctly detecting and identifying a major problem. An R package met implementing the proposed method is available on CRAN.

Patients With a History of a Cardiac Implantable Electronic Device Have a Higher Likelihood of 90-Day Cardiac Events After Total Joint Arthroplasty: A Matched Cohort Study

INTRODUCTION

We sought to identify the incidence of new 90-day cardiac events, 90-day mortality, 90-day unplanned readmissions, and 30-day emergency department (ED) visits after total joint arthroplasty (TJA) in patients with a history of a cardiac implantable electronic device (CIED) and compare these outcomes in TJA patients without a CIED.

METHODS

Kaiser Permanente's Cardiac Device and Total Joint Replacement Registries were used to identify elective primary TJA performed for osteoarthritis. TJA with a CIED was matched with TJA without a CIED (n = 365 pairs) on patient characteristics, demographics, and procedure type. A McNemar test was used to evaluate categorical outcomes.

RESULTS

Of the TJA with a CIED, there were 24 cardiac events (6.6%), 1 mortality (0.3%), 30 readmissions (8.2%), and 39 ED visits (10.7%). TJA patients with a CIED had a higher likelihood of cardiac events (odds ratio [OR] = 3.14, 95% confidence interval [CI] = 1.28 to 8.08). No difference was observed in mortality (OR = 0.50, 95% CI = 0.02 to 6.98), readmissions (OR = 1.26, 95% CI = 0.71 to 2.25), or ED visits (OR = 1.15, 95% CI = 0.71 to 1.88).

CONCLUSION

In our matched cohort study, TJA patients with a history of a CIED had a higher likelihood of incident 90-day cardiac events when compared with patients without a CIED without a difference observed for 90-day mortality, unplanned readmission, and 30-day ED visit.

LEVEL OF EVIDENCE

Level III.

The Association Between Tibial Slope and Revision Anterior Cruciate Ligament Reconstruction in Patients ≤21 Years Old: A Matched Case-Control Study Including 317 Revisions

BACKGROUND

There is evidence that tibial slope may play a role in revision risk after anterior cruciate ligament reconstruction (ACLR); however, prior studies are inconsistent.

PURPOSE

To determine (1) whether there is a difference in lateral tibial posterior slope (LTPS) or medial tibial posterior slope (MTPS) between patients undergoing revised ACLR and those not requiring revision and (2) whether the medial-to-lateral slope difference is different between these 2 groups.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

We conducted a matched case-control study (2006-2015). Cases were patients aged ≤21 years who underwent revision surgery after primary unilateral ACLR; controls were patients aged ≤21 years without revision who were identified from the same source population. Controls were matched to cases by age, sex, body mass index, race, graft type, femoral fixation device, and post-ACLR follow-up time. Tibial slope measurements were made by a single blinded reviewer using magnetic resonance imaging. The Wilcoxon signed rank test and McNemar test were used for continuous and categorical variables, respectively.

RESULTS

No difference was observed between revised and nonrevised ACLR groups for LTPS (median: 6° vs 6°, P = .973) or MTPS (median: 4° vs 5°, P = .281). Furthermore, no difference was found for medial-to-lateral slope difference (median: -1 vs -1, P = .289). A greater proportion of patients with revised ACLR had an LTPS ≥12° (7.6% vs 3.8%) and ≥13° (4.7% vs 1.3%); however, this was not statistically significant after accounting for multiple testing.

CONCLUSION

We failed to observe an association between revision ACLR surgery and LTPS, MTPS, or medial-to-lateral slope difference. However, there was a greater proportion of patients in the revision ACLR group with an LTPS ≥12°, suggesting that a minority of patients who have more extreme values of LTPS have a higher revision risk after primary ACLR. A future cohort study evaluating the angle that best differentiates patients at highest risk for revision is needed.

Comparing Resource Use in Medical Admissions of Children With Complex Chronic Conditions

BACKGROUND

Children with complex chronic conditions (CCCs) utilize a disproportionate share of hospital resources.

OBJECTIVE

We asked whether some hospitals display a significantly different pattern of resource utilization than others when caring for similar children with CCCs admitted for medical diagnoses.

RESEARCH DESIGN

Using Pediatric Health Information System data from 2009 to 2013, we constructed an inpatient Template of 300 children with CCCs, matching these to 300 patients at each hospital, thereby performing a type of direct standardization.

SUBJECTS

Children with CCCs were drawn from a list of the 40 most common medical principal diagnoses, then matched to patients across 40 Children's Hospitals.

MEASURES

Rate of intensive care unit admission, length of stay, resource cost.

RESULTS

For the Template-matched patients, when comparing resource use at the lower 12.5-percentile and upper 87.5-percentile of hospitals, we found: intensive care unit utilization was 111% higher (6.6% vs. 13.9%, P<0.001); hospital length of stay was 25% higher (2.4 vs. 3.0 d/admission, P<0.001); and finally, total cost per patient varied by 47% ($6856 vs. $10,047, P<0.001). Furthermore, some hospitals, compared with their peers, were more efficient with low-risk patients and less efficient with high-risk patients, whereas other hospitals displayed the opposite pattern.

CONCLUSIONS

Hospitals treating similar patients with CCCs admitted for similar medical diagnoses, varied greatly in resource utilization. Template Matching can aid chief quality officers benchmarking their hospitals to peer institutions and can help determine types of their patients having the most aberrant outcomes, facilitating quality initiatives to target these patients.

Practice Style Variation in Medicaid and Non-Medicaid Children With Complex Chronic Conditions Undergoing Surgery

OBJECTIVES

With differential payment between Medicaid and Non-Medicaid services, we asked whether style-of-practice differs between similar Medicaid and Non-Medicaid children with complex chronic conditions (CCCs) undergoing surgery.

SUMMARY OF BACKGROUND DATA

Surgery in children with CCCs accounts for a disproportionately large percentage of resource utilization at major children's hospitals.

METHODS

A matched cohort design, studying 23,582 pairs of children with CCCs undergoing surgery (Medicaid matched to Non-Medicaid within the same hospital) from 2009 to 2013 in 41 Children's Hospitals. Patients were matched on age, sex, principal procedure, CCCs, and other characteristics.

RESULTS

Median cost in Medicaid patients was $21,547 versus $20,527 in Non-Medicaid patients (5.0% higher, P < 0.001). Median paired difference in cost (Medicaid minus Non-Medicaid) was $320 [95% confidence interval (CI): $208, $445], (1.6% higher, P < 0.001). 90th percentile costs were $133,640 versus $127,523, (4.8% higher, P < 0.001). Mean paired difference in length of stay (LOS) was 0.50 days (95% CI: 0.36, 0.65), (P < 0.001). ICU utilization was 2.8% higher (36.7% vs 35.7%, P < 0.001). Finally, in-hospital mortality pooled across all pairs was higher in Medicaid patients (0.38% vs 0.22%, P = 0.002). After adjusting for multiple testing, no individual hospital displayed significant differences in cost between groups, only 1 hospital displayed significant differences in LOS and 1 in ICU utilization.

CONCLUSIONS

Treatment style differences between Medicaid and Non-Medicaid children were small, suggesting little disparity with in-hospital surgical care for patients with CCCs operated on within Children's Hospitals. However, in-hospital mortality, although rare, was slightly higher in Medicaid patients and merits further investigation.

Comparing Outcomes between Antibody Induction Therapies in Kidney Transplantation

Kidney transplant recipients often receive antibody induction. Previous studies of induction therapy were often limited by short follow-up and/or absence of information about complications. After linking Organ Procurement and Transplantation Network data with Medicare claims, we compared outcomes between three induction therapies for kidney recipients. Using novel matching techniques developed on the basis of 15 clinical and demographic characteristics, we generated 1:1 pairs of alemtuzumab-rabbit antithymocyte globulin (rATG) (5330 pairs) and basiliximab-rATG (9378 pairs) recipients. We used paired Cox regression to analyze the primary outcomes of death and death or allograft failure. Secondary outcomes included death or sepsis, death or lymphoma, death or melanoma, and healthcare resource utilization within 1 year. Compared with rATG recipients, alemtuzumab recipients had higher risk of death (hazard ratio [HR], 1.14; 95% confidence interval [95% CI], 1.03 to 1.26; P<0.01) and death or allograft failure (HR, 1.18; 95% CI, 1.09 to 1.28; P<0.001). Results for death as well as death or allograft failure were generally consistent among elderly and nonelderly subgroups and among pairs receiving oral prednisone. Compared with rATG recipients, basiliximab recipients had higher risk of death (HR, 1.08; 95% CI, 1.01 to 1.16; P=0.03) and death or lymphoma (HR, 1.12; 95% CI, 1.01 to 1.23; P=0.03), although these differences were not confirmed in subgroup analyses. One-year resource utilization was slightly lower among alemtuzumab recipients than among rATG recipients, but did not differ between basiliximab and rATG recipients. This observational evidence indicates that, compared with alemtuzumab and basiliximab, rATG associates with lower risk of adverse outcomes, including mortality.

Outcomes, ICU Use, and Length of Stay in Chronically Ill Black and White Children on Medicaid and Hospitalized for Surgery

BACKGROUND

With increasing Medicaid coverage, it has become especially important to determine whether racial differences exist within the Medicaid system. We asked whether disparities exist in hospital practice and patient outcomes between matched black and white Medicaid children with chronic conditions undergoing surgery.

STUDY DESIGN

We conducted a matched cohort study, matching 6,398 pairs within states on detailed patient characteristics using data from 25 states contributing adequate Medicaid Analytic eXtract claims for admissions of children with chronic conditions undergoing the same surgical procedures between January 1, 2009 and November 30, 2010 for ages 1 to 18 years.

RESULTS

The black patient 30-day revisit rate was 19.3% vs 19.8% in matched white patients (p = 0.61), 30-day readmission rates were 7.0% vs 6.9% (p = 0.43), and 30-day mortality rates were 0.38% vs 0.19% (p = 0.06), respectively. A higher percentage of black patients exceeded their own state's individual median length of stay (44.0% vs 39.6%; p < 0.001) and median ICU length of stay (25.9% vs 23.8%; p < 0.001). Intensive care unit use was higher in black patients (25.9% vs 23.8%; p < 0.001). After adjusting for multiple testing, only 2 states were found to differ significantly by race (New York for length of stay and New Jersey for ICU use).

CONCLUSIONS

We did not observe disparities in 30-day revisits and readmissions for chronically ill children in Medicaid undergoing surgery, and only slight differences in length of stay, ICU length of stay, and use of the ICU, where blacks displayed somewhat elevated rates compared with white controls.

Racial Disparities in Medicaid Asthma Hospitalizations

BACKGROUND AND OBJECTIVES

Black children with asthma comprise one-third of all asthma patients in Medicaid. With increasing Medicaid coverage, it has become especially important to monitor Medicaid for differences in hospital practice and patient outcomes by race.

METHODS

A multivariate matched cohort design, studying 11 079 matched pairs of children in Medicaid (black versus white matched pairs from inside the same state) admitted for asthma between January 1, 2009 and November 30, 2010 in 33 states contributing adequate Medicaid Analytic eXtract claims.

RESULTS

Ten-day revisit rates were 3.8% in black patients versus 4.2% in white patients (P = .12); 30-day revisit and readmission rates were also not significantly different by race (10.5% in black patients versus 10.8% in white patients; P = .49). Length of stay (LOS) was also similar; both groups had a median stay of 2.0 days, with a slightly lower percentage of black patients exceeding their own state's median LOS (30.2% in black patients versus 31.8% in white patients; P = .01). The mean paired difference in LOS was 0.00 days (95% confidence interval, -0.08 to 0.08). However, ICU use was higher in black patients than white patients (22.2% versus 17.5%; P < .001). After adjusting for multiple testing, only 4 states were found to differ significantly, but only in ICU use, where blacks had higher rates of use.

CONCLUSIONS

For closely matched black and white patients, racial disparities concerning asthma admission outcomes and style of practice are small and generally nonsignificant, except for ICU use, where we observed higher rates in black patients.

Practice Patterns in Medicaid and Non-Medicaid Asthma Admissions

BACKGROUND AND OBJECTIVES

With American children experiencing increased Medicaid coverage, it has become especially important to determine if practice patterns differ between Medicaid and non-Medicaid patients. Auditing such potential differences must carefully compare like patients to avoid falsely identifying suspicious practice patterns. We asked if we could observe differences in practice patterns between Medicaid and non-Medicaid patients admitted for asthma inside major children's hospitals.

METHODS

A matched cohort design, studying 17 739 matched pairs of children (Medicaid to non-Medicaid) admitted for asthma in the same hospital between April 1, 2011 and March 31, 2014 in 40 Children's Hospital Association hospitals contributing data to the Pediatric Hospital Information System database. Patients were matched on age, sex, asthma severity, and other patient characteristics.

RESULTS

Medicaid patient median cost was $4263 versus $4160 for non-Medicaid patients (P < .001). Additionally, the median cost difference (Medicaid minus non-Medicaid) between individual pairs was only $84 (95% confidence interval: 44 to 124), and the mean cost difference was only $49 (95% confidence interval: -72 to 170). The 90th percentile costs were also similar between groups ($10 710 vs $10 948; P < .07). Length of stay (LOS) was also very similar; both groups had a median stay of 1 day, with a similar percentage of patients exceeding the 90th percentile of individual hospital LOS (7.1% vs 6.7%; P = .14). ICU use was also similar (10.1% vs 10.6%; P = .12).

CONCLUSIONS

For closely matched patients within the same hospital, Medicaid status did not importantly influence costs, LOS, or ICU use.

Effects of Cancer Stage and Treatment Differences on Racial Disparities in Survival From Colon Cancer: A United States Population-Based Study

BACKGROUND & AIMS

We evaluated differences in treatment of black vs white patients with colon cancer and assessed their effects on survival, based on cancer stage.

METHODS

We collected data from the Surveillance, Epidemiology, and End Results-Medicare database and identified 6190 black and 61,951 white patients with colon cancer diagnosed from 1998 through 2009 and followed up through 2011. Three sets of 6190 white patients were matched sequentially, using a minimum distance strategy, to the same set of 6190 black patients based on demographic (age; sex; diagnosis year; and Surveillance, Epidemiology, and End Results registry), tumor presentation (demographic plus comorbidities, tumor stage, grade, and size), and treatment (presentation plus therapies) variables. We conducted sensitivity analyses to explore the effects of socioeconomic status in a subcohort that included 2000 randomly selected black patients. Racial differences in treatment were assessed using a logistic regression model; their effects on racial survival disparity were evaluated using the Kaplan-Meier method and the Cox proportional hazards model.

RESULTS

After patients were matched for demographic variables, the absolute 5-year difference in survival between black and white patients was 8.3% (white, 59.2% 5-y survival; blacks, 50.9% 5-y survival) (P < .0001); this value decreased significantly, to 5.0% (P < .0001), after patients were matched for tumor presentation, and decreased to 4.9% (P < .0001) when patients were matched for treatment. Differences in treatment therefore accounted for 0.1% of the 8.3% difference in survival between black and white patients. After patients were matched for tumor presentation, racial disparities were observed in almost all types of treatment; the disparities were most prominent for patients with advanced-stage cancer (stages III or IV, up to an 11.1% difference) vs early stage cancer (stages I or II, up to a 4.3% difference). After patients were matched for treatment, there was a greater reduction in disparity for black vs white patients with advanced-stage compared with early-stage cancer. In sensitivity analyses, the 5-year racial survival disparity was 7.7% after demographic match, which was less than the 8.3% observed in the complete cohort. This reduction likely was owing to the differences between the subcohort and the complete cohort in those variables that were not included in the demographic match. This value was reduced to 6.5% (P = .0001) after socioeconomic status was included in the demographic match. The difference decreased significantly to 2.8% (P = .090) after tumor presentation match, but was not reduced further after treatment match.

CONCLUSIONS

We observed significant disparities in treatment and survival of black vs white patients with colon cancer. The disparity in survival appears to have been affected more strongly by tumor presentation at diagnosis than treatment. The effects of treatment differences on disparities in survival were greater for patients with advanced-stage vs early-stage cancer.

E-Cigarette Use and Intention to Initiate or Quit Smoking Among US Youths

OBJECTIVES

We assessed whether e-cigarette use is associated with (1) intention to smoke cigarettes among never-smoking youths and youth experimenters, and (2) intention to quit smoking among current youth smokers.

METHODS

We categorized participants from the 2012 National Youth Tobacco Survey data (n = 20 193) as never-smoking youth (n = 16 238), youth experimenters (n = 3248), and current youth smokers (n = 707). We matched groups on the basis of a propensity score comprising covariates predicting e-cigarette use.

RESULTS

E-cigarette users who had never smoked cigarettes (adjusted odds ratio [AOR] = 3.62; 95% confidence interval [CI] = 2.04, 6.45) and who had experimented with smoking (AOR = 1.99; 95% CI = 1.50, 2.64) had elevated intention to smoke cigarettes compared with their counterparts who had never used e-cigarettes. We did not find any significant association between e-cigarette use and intention to quit smoking among current youth smokers (P = .33).

CONCLUSIONS

E-cigarette use among US youths is associated with intention to smoke but not with intention to quit smoking.

Examining Causes of Racial Disparities in General Surgical Mortality: Hospital Quality Versus Patient Risk

BACKGROUND

Racial disparities in general surgical outcomes are known to exist but not well understood.

OBJECTIVES

To determine if black-white disparities in general surgery mortality for Medicare patients are attributable to poorer health status among blacks on admission or differences in the quality of care provided by the admitting hospitals.

RESEARCH DESIGN

Matched cohort study using Tapered Multivariate Matching.

SUBJECTS

All black elderly Medicare general surgical patients (N=18,861) and white-matched controls within the same 6 states or within the same 838 hospitals.

MEASURES

Thirty-day mortality (primary); others include in-hospital mortality, failure-to-rescue, complications, length of stay, and readmissions.

RESULTS

Matching on age, sex, year, state, and the exact same procedure, blacks had higher 30-day mortality (4.0% vs. 3.5%, P<0.01), in-hospital mortality (3.9% vs. 2.9%, P<0.0001), in-hospital complications (64.3% vs. 56.8% P<0.0001), and failure-to-rescue rates (6.1% vs. 5.1%, P<0.001), longer length of stay (7.2 vs. 5.8 d, P<0.0001), and more 30-day readmissions (15.0% vs. 12.5%, P<0.0001). Adding preoperative risk factors to the above match, there was no significant difference in mortality or failure-to-rescue, and all other outcome differences were small. Blacks matched to whites in the same hospital displayed no significant differences in mortality, failure-to-rescue, or readmissions.

CONCLUSIONS

Black and white Medicare patients undergoing the same procedures with closely matched risk factors displayed similar mortality, suggesting that racial disparities in general surgical mortality are not because of differences in hospital quality. To reduce the observed disparities in surgical outcomes, the poorer health of blacks on presentation for surgery must be addressed.

Large, Sparse Optimal Matching with Refined Covariate Balance in an Observational Study of the Health Outcomes Produced by New Surgeons

Every newly trained surgeon performs her first unsupervised operation. How do the health outcomes of her patients compare with the patients of experienced surgeons? Using data from 498 hospitals, we compare 1252 pairs comprised of a new surgeon and an experienced surgeon working at the same hospital. We introduce a new form of matching that matches patients of each new surgeon to patients of an otherwise similar experienced surgeon at the same hospital, perfectly balancing 176 surgical procedures and closely balancing a total of 2.9 million categories of patients; additionally, the individual patient pairs are as close as possible. A new goal for matching is introduced, called "refined covariate balance," in which a sequence of nested, ever more refined, nominal covariates is balanced as closely as possible, emphasizing the first or coarsest covariate in that sequence. A new algorithm for matching is proposed and the main new results prove that the algorithm finds the closest match in terms of the total within-pair covariate distances among all matches that achieve refined covariate balance. Unlike previous approaches to forcing balance on covariates, the new algorithm creates multiple paths to a match in a network, where paths that introduce imbalances are penalized and hence avoided to the extent possible. The algorithm exploits a sparse network to quickly optimize a match that is about two orders of magnitude larger than is typical in statistical matching problems, thereby permitting much more extensive use of fine and near-fine balance constraints. The match was constructed in a few minutes using a network optimization algorithm implemented in R. An R package called rcbalance implementing the method is available from CRAN.

Erythropoiesis stimulating agents and clinical outcomes of invasive breast cancer patients receiving cytotoxic chemotherapy

The use of erythropoiesis stimulating agents (ESAs) to treat anemia in breast cancer patients who are treated with chemotherapy is a matter of ongoing debate. Several recent randomized trials challenged conventional wisdom, which holds that ESAs are contraindicated for breast cancer patients undergoing curative treatment. We aimed to perform the first large national population-based study to analyze the association between ESA use and breast cancer patient outcomes. Cytotoxic chemotherapy-treated invasive breast cancer patients were identified from the Surveillance, Epidemiology, and End Results (SEER)-Medicare database. Non-ESA users were sequentially 1:1 matched to 2,000 randomly sampled ESA users on demographics (age, diagnosis year, race, marital status, and socioeconomic status), tumor presentation (stage, grade, and status of hormone receptors), and treatments (surgery, radiation, and sub-types of chemotherapy) using a minimum distant strategy. Breast cancer-specific survival of ESA and matched non-ESA users was compared using Fine and Gray competing risk model. Compared to ESA users, non-ESA users exhibited dramatically different baseline characteristics such as less advanced tumor, and fewer co-morbidities. Non-ESA users had a significantly more favorable breast cancer-specific survival (subdistribution hazard ratio [sHR] = 0.75, p < 0.0001). This survival disparity was progressively diminished in the sequential matching of demographics (sHR = 0.74, p = 0.0004), presentation (sHR = 0.86, p = 0.06), and treatment (sHR = 0.89, p = 0.17) variables. Stratified analyses identified subgroups of patients whose breast cancer-specific survival were not different between ESA and non-ESA users. In the SEER-Medicare database, ESA usage does not seem to be associated with unfavorable breast cancer-specific survival in breast cancer patients receiving cytotoxic chemotherapy. The ESA-breast cancer prognosis association is complex and requires more intensive investigations.

A hospital-specific template for benchmarking its cost and quality

OBJECTIVE

Develop an improved method for auditing hospital cost and quality tailored to a specific hospital's patient population.

DATA SOURCES/SETTING

Medicare claims in general, gynecologic and urologic surgery, and orthopedics from Illinois, New York, and Texas between 2004 and 2006.

STUDY DESIGN

A template of 300 representative patients from a single index hospital was constructed and used to match 300 patients at 43 hospitals that had a minimum of 500 patients over a 3-year study period.

DATA COLLECTION/EXTRACTION METHODS

From each of 43 hospitals we chose 300 patients most resembling the template using multivariate matching.

PRINCIPAL FINDINGS

We found close matches on procedures and patient characteristics, far more balanced than would be expected in a randomized trial. There were little to no differences between the index hospital's template and the 43 hospitals on most patient characteristics yet large and significant differences in mortality, failure-to-rescue, and cost.

CONCLUSION

Matching can produce fair, directly standardized audits. From the perspective of the index hospital, "hospital-specific" template matching provides the fairness of direct standardization with the specific institutional relevance of indirect standardization. Using this approach, hospitals will be better able to examine their performance, and better determine why they are achieving the results they observe.

Mortality and cardiovascular disease among older live kidney donors

Over the past two decades, live kidney donation by older individuals (≥55 years) has become more common. Given the strong associations of older age with cardiovascular disease (CVD), nephrectomy could make older donors vulnerable to death and cardiovascular events. We performed a cohort study among older live kidney donors who were matched to healthy older individuals in the Health and Retirement Study. The primary outcome was mortality ascertained through national death registries. Secondary outcomes ascertained among pairs with Medicare coverage included death or CVD ascertained through Medicare claims data. During the period from 1996 to 2006, there were 5717 older donors in the United States. We matched 3368 donors 1:1 to older healthy nondonors. Among donors and matched pairs, the mean age was 59 years; 41% were male and 7% were black race. In median follow-up of 7.8 years, mortality was not different between donors and matched pairs (p = 0.21). Among donors with Medicare, the combined outcome of death/CVD (p = 0.70) was also not different between donors and nondonors. In summary, carefully selected older kidney donors do not face a higher risk of death or CVD. These findings should be provided to older individuals considering live kidney donation.

Template matching for auditing hospital cost and quality

OBJECTIVE

Develop an improved method for auditing hospital cost and quality.

DATA SOURCES/SETTING

Medicare claims in general, gynecologic and urologic surgery, and orthopedics from Illinois, Texas, and New York between 2004 and 2006.

STUDY DESIGN

A template of 300 representative patients was constructed and then used to match 300 patients at hospitals that had a minimum of 500 patients over a 3-year study period.

DATA COLLECTION/EXTRACTION METHODS

From each of 217 hospitals we chose 300 patients most resembling the template using multivariate matching.

PRINCIPAL FINDINGS

The matching algorithm found close matches on procedures and patient characteristics, far more balanced than measured covariates would be in a randomized clinical trial. These matched samples displayed little to no differences across hospitals in common patient characteristics yet found large and statistically significant hospital variation in mortality, complications, failure-to-rescue, readmissions, length of stay, ICU days, cost, and surgical procedure length. Similar patients at different hospitals had substantially different outcomes.

CONCLUSION

The template-matched sample can produce fair, directly standardized audits that evaluate hospitals on patients with similar characteristics, thereby making benchmarking more believable. Through examining matched samples of individual patients, administrators can better detect poor performance at their hospitals and better understand why these problems are occurring.

Racial disparities in operative procedure time: the influence of obesity

BACKGROUND

Using Pennsylvania Medicare claims from 1995 to 1996, the authors previously reported that anesthesia procedure length appears longer in blacks than whites. In a new study using a different and larger data set, the authors now examine whether body mass index (BMI), not available in Medicare claims, explains this difference. The authors also examine the relative contributions of surgical and anesthesia times.

METHODS

The Obesity and Surgical Outcomes Study of 47 hospitals throughout Illinois, New York, and Texas abstracted chart information including BMI on elder Medicare patients (779 blacks and 14,596 whites) undergoing hip and knee replacement and repair, colectomy, and thoracotomy between 2002 and 2006. The authors matched all black Medicare patients to comparable whites and compared procedure lengths.

RESULTS

Mean BMI in the black and white populations was 30.24 and 28.96 kg/m, respectively (P<0.0001). After matching on age, sex, procedure, comorbidities, hospital, and BMI, mean white BMI in the comparison group was 30.1 kg/m (P=0.94). The typical matched pair difference (black-white) in anesthesia (induction to recovery room) procedure time was 7.0 min (P=0.0019), of which 6 min reflected the surgical (cut-to-close) time difference (P=0.0032). Within matched pairs, where the difference in procedure times was greater than 30 min between patients, blacks more commonly had longer procedure times (Odds=1.39; P=0.0008).

CONCLUSIONS

Controlling for patient characteristics, BMI, and hospital, elder black Medicare patients experienced slightly but significantly longer procedure length than their closely matched white controls. Procedure length difference was almost completely due to surgery, not anesthesia.

Effect of the 2010 Chilean earthquake on posttraumatic stress: reducing sensitivity to unmeasured bias through study design

In 2010, a magnitude 8.8 earthquake hit Chile, devastating parts of the country. Having just completed its national socioeconomic survey, the Chilean government reinterviewed a subsample of respondents, creating unusual longitudinal data about the same persons before and after a major disaster. The follow-up evaluated posttraumatic stress symptoms (PTSS) using Davidson's Trauma Scale. We use these data with two goals in mind. Most studies of PTSS after disasters rely on recall to characterize the state of affairs before the disaster. We are able to use prospective data on preexposure conditions, free of recall bias, to study the effects of the earthquake. Second, we illustrate recent developments in statistical methodology for the design and analysis of observational studies. In particular, we use new and recent methods for multivariate matching to control 46 covariates that describe demographic variables, housing quality, wealth, health, and health insurance before the earthquake. We use the statistical theory of design sensitivity to select a study design with findings expected to be insensitive to small or moderate biases from failure to control some unmeasured covariate. PTSS were dramatically but unevenly elevated among residents of strongly shaken areas of Chile when compared with similar persons in largely untouched parts of the country. In 96% of exposed-control pairs exhibiting substantial PTSS, it was the exposed person who experienced stronger symptoms (95% confidence interval = 0.91-1.00).

Obesity and readmission in elderly surgical patients

BACKGROUND

Reducing readmissions has become a focus in efforts by Medicare to improve health care quality and reduce costs. This study aimed to determine whether causes for readmission differed between obese and nonobese patients, possibly allowing for targeted interventions.

METHODS

A matched case control study of Medicare patients admitted between 2002 and 2006 who were readmitted after hip or knee surgery, colectomy, or thoracotomy was performed. Patients were matched exactly for procedure, while also balancing on hospital, age, and sex. Conditional logistic regression was used to study the odds of readmission for very obese cases (body mass index >35 kg/m2) versus normal weight patients (body mass index of 20-30 kg/m2) after also controlling for race, transfer-in and emergency status, and comorbidities.

RESULTS

Among 15,914 patient admissions, we identified 1,380 readmitted patients and 2,760 controls. The risk of readmission was increased for obese compared to nonobese patients both before and after controlling for comorbidities (before: odds ratio, 1.35; P = .003; after: odds ratio, 1.25; P = .04). Reasons for readmission varied by procedure but were not different by body mass index category.

CONCLUSION

Obese patients have an increased risk of readmission, yet the reasons for readmission in obese patients appear to be similar to those for nonobese patients, suggesting that improved postdischarge management for the obese cannot focus on a few specific causes of readmission but must instead provide a broad range of interventions.

Contrasting Evidence Within and Between Institutions That Provide Treatment in an Observational Study of Alternate Forms of Anesthesia

In a randomized trial, subjects are assigned to treatment or control by the flip of a fair coin. In many nonrandomized or observational studies, subjects find their way to treatment or control in two steps, either or both of which may lead to biased comparisons. By a vague process perhaps affected by proximity or sociodemographic issues, subjects find their way to institutions that provide treatment. Once at such an institution, a second process, perhaps thoughtful and deliberate, assigns individuals to treatment or control. In the current paper, the institutions are hospitals, and the treatment under study is the use of general anesthesia alone versus some use of regional anesthesia during surgery. For a specific operation, the use of regional anesthesia may be typical in one hospital and atypical in another. A new matched design is proposed for studies of this sort, one that creates two types of nonoverlapping matched pairs. Using a new extension of optimal matching with fine balance, pairs of the first type exactly balance treatment assignment across institutions, so each institution appears in the treated group with the same frequency that it appears in the control group; hence, differences between institutions that affect everyone in the same way cannot bias this comparison. Pairs of the second type compare institutions that assign most subjects to treatment and other institutions that assign most subjects to control, so each institution is represented in the treated group if it typically assigns subjects to treatment or alternatively in the control group if it typically assigns subjects to control, and no institution appears in both groups. By and large, in the second type of matched pair, subjects became treated subjects or controls by choosing an institution, not by a thoughtful and deliberate process of selecting subjects for treatment within institutions. The design provides two evidence factors, that is, two tests of the null hypothesis of no treatment effect that are independent when the null hypothesis is true, where each factor is largely unaffected by certain unmeasured biases that could readily invalidate the other factor. The two factors permit separate and combined sensitivity analyses, where the magnitude of bias affecting the two factors may differ. The case of knee surgery in the study of regional versus general anesthesia is considered in detail.