In a randomized experiment comparing two treatments, there is interference between units if applying the treatment to one unit may affect other units. Interference implies that effects are not comparisons of potential responses exhibit, under and control, but instead inherently more complex. common in social settings where people communicate, compete, or spread disease; studies treat part an organism using symmetrical as control; apply different treatments same at times; many situations....

The Accreditation Council for Graduate Medical Education (ACGME) implemented duty hour regulations physicians-in-training throughout the United States on July 1, 2003. association of reform with mortality among patients in teaching hospitals nationally has not been well established.To determine whether change was associated relative changes Medicare different intensity.An observational study all unique (N = 8 529 595) admitted to short-term, acute-care, general US nonfederal 3321) using...

More than 300,000 hip fractures occur each year in the United States. Recent practice guidelines have advocated greater use of regional anesthesia for fracture surgery.To test association (ie, spinal or epidural) vs general with 30-day mortality and hospital length stay after fracture.We conducted a matched retrospective cohort study involving patients 50 years older who were undergoing surgery at acute care hospitals New York State between July 1, 2004, December 31, 2011. Our main analysis...

Latent variable models represent the joint distribution of observable variables in terms a simple structure involving unobserved or latent variables, usually assuming conditional independence given variables. These play an important role educational measurement and psychometrics, sociology population genetics, are implicit some work on systems reliability. We study broad class models, namely monotone unidimensional which is scalar, conditionally independent observables stochastically...

Summary A new test is proposed comparing two multivariate distributions by using distances between observations. Unlike earlier tests interpoint distances, the statistic has a known exact distribution and exactly free. The are used to construct an optimal non-bipartite matching, i.e. matching of observations into disjoint pairs minimize total distance within pairs. cross-match number containing one observation from first second. Distributions that very different will exhibit few...

▪ In observational studies or nonrandomized experiments, treated and control groups may differ in their outcomes even if the treatment has no effect; this happen were not comparable before start of treatment. The fail to be either two ways: They with respect characteristics that have been measured, which case there is an overt bias, they ways a hidden bias. Overt biases are controlled through adjustments, such as matching. Hidden bias more difficult address because relevant measurements...

An observational study is an attempt to estimate the effects of a treatment when subjects are not randomly assigned or control. The possibility using more than one control group has often been briefly mentioned in general discussions studies, and many studies have used two groups. Here, limited dispersed literature on this subject reviewed, topic developed several directions by formal notation for studies. value second depends supplementary information that available about unobserved biases...

In observational studies, treatments are not randomly assigned to experimental units, so that randomization tests and their associated interval estimates generally applicable. an effort compensate for the lack of randomization, treated control units often matched on basis observed covariates; however, possibility remains bias due residual imbalances in unobserved covariates. A general though simple method is proposed displaying sensitivity permutation inferences a range assumptions about...

Abstract In a model, such as logit regression we wish to compare the relative importance of two groups predictors for various objectives. example that motivated this work, model predicts patient outcomes during hospital stays, and measure contribution characteristics variation in among patients hospitals. This is done using dispersion contributions fitted outcomes. As seen, question distinct from other common questions, including quality overall fit, degree which outcome accurately...

Abstract An instrument is a random nudge toward acceptance of treatment that affects outcomes only to the extent it treatment. Nonetheless, in settings which assignment mostly deliberate and not random, there may exist some essentially nudges accept treatment, so use an might extract bits from setting otherwise quite biased its assignments. weak if barely influence or strong are often decisive influencing assignment. Although ideally ostensibly perfectly biased, possible be certain this;...

In observational studies of treatment effects, matched samples have traditionally been constructed using two tools, namely close matches on one or key covariates and the propensity score to stochastically balance large numbers covariates. Here we propose a third tool, fine balance, obtained assignment algorithm in new way. We use all three tools construct sample for an ongoing study provider specialty ovarian cancer. Fine refers exact nominal covariate, often with many categories, but it...

Using a small example as an illustration, this article reviews multivariate matching from the perspective of working scientist who wishes to make effective use available methods. The several goals are discussed. Matching tools reviewed, including propensity scores, covariate distances, fine balance, and related methods such near-fine refined exact near-exact matching, tactics addressing missing values, entire number, checks balance. structures described, with variable number controls, full...

Conventionally, the construction of a pair-matched sample selects treated and control units pairs them in single step with view to balancing observed covariates $\mathbf{x}$ reducing heterogeneity or dispersion treated-minus-control response differences, $Y$. In contrast, method cardinality matching developed here first maximum number subject covariate balance constraints and, balanced for hand, then separately minimize Reduced pair differences responses $Y$ is known reduce sensitivity...

Every newly trained surgeon performs her first unsupervised operation. How do the health outcomes of patients compare with experienced surgeons? Using data from 498 hospitals, we 1252 pairs comprised a new and an working at same hospital. We introduce form matching that matches each to otherwise similar hospital, perfectly balancing 176 surgical procedures closely total 2.9 million categories patients; additionally, individual patient are as close possible. A goal for is introduced, called...

The literature suggests that hospitals with better nursing work environments provide quality of care. Less is known about value (cost vs quality).To test whether displayed than those worse and to determine patient risk groups associated the greatest value.A retrospective matched-cohort design, comparing outcomes cost patients at focal recognized nationally as having good nurse working nurse-to-bed ratios 1 or greater control group without such recognition less 1. This study included 25 752...

Policy Points Patients with low socioeconomic status (SES) experience poorer survival rates after diagnosis of breast cancer, even when enrolled in Medicare and Medicaid. Most the difference is due to more advanced cancer on presentation general poor health lower SES patients, while only a very small fraction disparity differences treatment. Even comparing low‐ versus not‐low‐SES whites (without confounding by race) between disparate white populations large associated use preventive care,...

In a randomized experiment, the investigator creates clear and relatively unambiguous comparison of treatment groups by exerting tight control over assignment treatments to experimental subjects, ensuring that comparable subjects receive alternative treatments. an observational study, lacks assignments must seek in other ways. Care choice circumstances which study is conducted can greatly influence quality evidence about effects. This illustrated detail using three studies use effectively,...

Background. Outcomes studies often need a level of detail that is not present in administrative data, therefore requiring abstraction medical charts. Case-control methods may be used to improve statistical power and reduce costs, but limitations exact matching preclude the use many covariates. Unlike matching, multivariate allow cases matched simultaneously on hundreds Objectives. To develop case-control pairs study death after surgery Medicare population. Research Design. Using 830 randomly...

Summary Huber's m‐estimates use an estimating equation in which observations are permitted a controlled level of influence. The family includes least squares and maximum likelihood, but typical applications give extreme limited weight. Maritz proposed methods exact approximate permutation inference for m‐tests, confidence intervals, estimators, can be derived from random assignment paired subjects to treatment or control. In contrast, observational studies, where treatments not randomly...