Life Tables

A life table or a mortality table represents the survival patterns of a population.

It comprises multiple columns, each serving a practical purpose, starting with time intervals in the first column.

The second column lists the number of individuals, patients, or subjects at the start of the study, and the third column lists those who died during the interval.

The fourth column indicates the number of people missing follow-ups, and the fifth column shows the number of people who withdrew alive during the interval.

The sixth column presents the effective number of participants exposed to the risk under study.

The count is considered effective because it adjusts for the participants who were either withdrawn alive or lost to follow-up, assuming that withdrawals happen uniformly throughout the interval.

It is typically estimated that withdrawals occur midway through the interval, leading to a reduction by half in the denominator for calculating risks.

The following two columns are conditional probabilities of death and survival. They are typically calculated as follows.

Finally, the last column measures cumulative survival rates across all intervals.