# Life Tables

*Lead Author(s):* Jeff Martin, MD
## Definition of Life Tables

Life tables, as the name implies, were first constructed to look at the cumulative survival (mortality) of large populations over a lifetime. So they used both large numbers of persons and long time periods.
## Key Difference from Kaplan-Meier Method - Do Not Need the Date of Each Event

**Key difference from Kaplan-Meier is that probabilities are calculated for fixed time intervals, not at the exact time of each event**
Life tables differ from a Kaplan-Meier analysis in that they do not require knowing the exact time of each death (event).
## Life Tables Do Use Discrete Intervals

**A life table also divides time up into discrete pieces,** calculating survival probabilities for each piece, and obtaining a cumulative incidence by multiplying the individual probabilities together. But the time pieces are arbitrary, not determined by the time of each death (event). Hence, the lack of a need to know the time of each death (event). The time intervals are set by the investigator. For a lifetime life table they are typically 5-year intervals. For a cohort study, 1-year or 6-month intervals might be more typical.
## Similarities Between Kaplan-Meier and Life Tables

**For large data sets the life table and the Kaplan-Meier method produce nearly the same results**