When comparing survival times between two treatment groups, it may be more appropriate to compare the restricted mean lifetime, i.e., the expectation of lifetime restricted to a time L, rather than mean lifetime in order to accommodate censoring. When the treatments are not assigned to patients randomly, as in observational studies, we also need to account for treatment imbalances in confounding factors. In this article, we propose estimators for the difference of the restricted mean lifetime between two groups that account for treatment imbalances in prognostic factors assuming a proportional hazards relationship. Large-sample properties of our estimators based on martingale theory for counting processes are also derived. Simulation studies were conducted to compare these estimators and to assess the adequacy of the large-sample approximations. Our methods are also applied to an observational database of acute coronary syndrome patients from Duke University Medical Center to estimate the treatment effect on the restricted mean lifetime over 5 years.

In designing longitudinal studies, researchers must determine the number of subjects to randomize based on the power to detect a clinically meaningful treatment difference and a proposed analysis plan. In this paper, we present formulas for sample size estimation and an assessment of statistical power for a two-treatment repeated measures design allowing for subject attrition. These formulas can be used for comparing two treatment groups across time in terms of linear contrasts. Subjects are assumed to drop out of the study at random so that the missing data do not alter the parameters of interest.

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OEGylated cyclodextrin-threaded polyrotaxanes (PRXs) capped with UV-cleavable stoppers were synthesized, and their thermoresponsive and degradable behavior were investigated. These PRXs in aqueous solutions exhibit fast thermally induced phase transitions and small hysteresis as well as tunable phase transition temperatures, which are quite distinct from previous methylated PRXs. Based on the mechanically interlocked architecture, PRXs are stable in solutions but can be completely degraded into hydrophilic components upon UV cleavage of stoppers. As a consequence, the thermoresponsive behavior of PRXs was switched off. Furthermore, micrometer-scale globular aggregates were formed from thermoresponsive PRXs above their phase transition temperatures but disaggregated quickly upon cooling or UV irradiation. This phenomenon was utilized to take these PRXs as unique carriers for guests with dually controlled release by both temperature and light. The present work provides efficient synthesis of a new class of thermoresponsive interlocked polymers with on-demand degradation, and the findings illustrate the prominent effect of PRX architecture on the remarkable thermoresponsive and degradable behavior.

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