caa a22 4500 605475989 CHVBK 20210128100354.0 cr unu---uuuuu 210128e20150101xx s 000 0 eng 10.1007/s10985-014-9291-y doi (NATIONALLICENCE)springer-10.1007/s10985-014-9291-y Zhang Min Department of Biostatistics, University of Michigan, 48109-2029, Ann Arbor, MI, USA aut Robust methods to improve efficiency and reduce bias in estimating survival curves in randomized clinical trials [Elektronische Daten] [Min Zhang] In randomized clinical trials, improving efficiency and reducing bias due to chance imbalance in covariates among groups are always of considerable interest. The two purposes are often achieved by some type of covariate adjustment. In trials involving time-to-an-event, Kaplan-Meier and Nelson-Aalen estimators are the most popular nonparametric estimation of survival curves. However, these methods do not permit direct covariate adjustment, missing the important chance of improving efficiency and reducing bias. In this article, we propose robust, covariate adjusted analogues of the Nelson-Aalen and Kaplan-Meier estimators. The method is robust in that it does not require any additional modeling assumptions and hence the resulting estimators are again nonparametric. The robustness is achieved by taking advantage of the study design, i.e., treatments are randomized. Large-sample properties of the proposed estimators are developed, which show that the improvement in efficiency is guaranteed asymptotically. Simulation studies using reasonably small sample sizes further demonstrate the efficiency gain and the ability to reduce or remove bias resulted from chance imbalance to a large degree, e.g., more than 10-fold reduction in bias is achieved. Efficiency improvement and bias reduction are also illustrated by application to a cancer clinical trial. The proposed methods may help to resolve the tension between the need to make best use of data and the unwillingness to make additional assumptions in analyzing data from clinical trials. Springer Science+Business Media New York, 2014 Covariate-adjustment nationallicence Nelson-Aalen estimator nationallicence Kaplan-Meier curve nationallicence Cumulative hazard function nationallicence Time-to-event nationallicence Lifetime Data Analysis Springer US; http://www.springer-ny.com 21/1(2015-01-01), 119-137 1380-7870 21:1<119 2015 21 10985 https://doi.org/10.1007/s10985-014-9291-y text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s10985-014-9291-y text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Zhang Min Department of Biostatistics, University of Michigan, 48109-2029, Ann Arbor, MI, USA aut NATIONALLICENCE 773 0- Lifetime Data Analysis Springer US; http://www.springer-ny.com 21/1(2015-01-01), 119-137 1380-7870 21:1<119 2015 21 10985