A life table describes the survival of a hypothetical group of persons from birth, through successive ages, to the death of the last member. In doing so, it shows the implications of a set of age-specific mortality rates for the probability of surviving from one age to another, and provides useful summary measures such as the expectation of life at birth. Beyond its wide use in studies of mortality, the life table has been used in studies of marriage, divorce, contraceptive use, and many other topics where it is valuable to examine how rates of decrement reduce the number of persons in a closed group.