ABSTRACT
Survival analysis or time-to-event analysis is a branch of statistics dealing with death or degradation in biological organisms, mechanical or electronic systems, or other areas. In survival analysis, censorings can be considered as a special type of missing data. Survival data can involve different types of censoring: left-censoring if a data point is equal to or below a certain value but it is unknown by how much; and right-censoring if a data point is a certain value but it is unknown by how much. The notion of frailty provides a convenient way to introduce random effects, association and unobserved heterogeneity into models for survival data. Modeling survival data can be based on a parametric or nonparametric method. One of the main goals of the landmark method is to estimate in an unbiased way the time-to-event probabilities in each group conditional on the group membership of patients at a specific, landmark time point.
