If the study period is long enough to observe the survival time of all subjects, as in some animal experiments, one may prefer to use more common methods, such as the t-test and ordinary least square regression, to analyse survival time as a continuous variable. However, in studies of human subjects there often is censoring and the outcome cannot be analysed by the usual methods for continuous data.

Subjects are often censored at different times, leading to unequal follow-up time. Analysis of the probability of survival during the study period as a dichotomous variable (alive vs dead), e.g. by a Chi-square test, would fail to account for this non-comparability between subjects.