[Interpretation and Application of Restricted Mean Survival Time].

Many clinical research and studies evaluate a time-to-event data, illustrate survival curves, and conventionally report an estimated hazard ratio to express the magnitude of the treatment effect when comparing between groups. However, it may not be straightforward to interpret the hazard ratio clinically and statistically when the proportional hazards assumption is invalid. In some recent papers published in clinical journals, the use of restricted mean survival time(RMST)or t-year mean survival time is discussed as one of the alternative summary measures for the time-to-event data. The RMST is defined as the expected value of time-to-event limited to a specific time point corresponding to the area under the survival curve up to the specific time point. This article summarizes the necessary information to conduct statistical analysis using the RMST, including the definition and statistical properties of the RMST, and clinical and statistical meaning and interpretation as compared with other summary measures of time-to-event data by application examples.