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# Life Tables

## 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

Topic revision: r3 - 03 Jun 2009 - 12:14:14 - MaryB?

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