changes (in terms of decades) of a population’s age structure. Historians use them,
too, to find significant information based on past population pyramids.What is a life table?
A life table is a statistical chart of mortality and survivorship of a group of people (also
called a cohort) of the same age at each “stage” of life. The results are usually shown
as the probability of death and survival, as well as the life expectancy at various ages.
There are two basic life tables, or expectations of life charts. A current (period or
cross-sectional) life table is based on age-specific mortality rates for a given period
(either a single or many years). It assumes that as a group ages it has a set pattern of
age-specific mortality rates that never change from year to year. But this is based on a
hypothetical model of mortality, not the true mortality of the cohort.
In a cohort (longitudinal or generation) life table, the people in the group are
well-defined, usually of the same age (such as all the people are born in 2000), and
have common experiences or exposures. Thus, it is based on age-specific mortality
rates that allow for known or projected changes in mortality in later years. (If the
group is followed up for the incidence of diseases, for example, such as osteoporosis or
heart disease development, it is called a cohort or prospective study.)
To compare, a current life table of life expectancy at age 65 in 2000 would be
worked out using the mortality rate for age 65 in 2000, for age 66 in 2000, for age 67
in 2000, and so on. A cohort life table of life expectancy at age 65 in 2000 would be
worked out using the mortality rate for age 65 in 2000, for age 66 in 2001, for age 67
in 2002, and so on. But note that not all cohorts are used in mortality studies. Some
are also used for other reasons, such as a professor following a cohort of students who
382 study together for the length of a certain degree program.
What are some of the statistical data
gathered during the periodic United States census?E
very ten years, the U.S. government takes a census that gathers important
statistical data about the entire population. In the 2000 census, this included
place of residence, age, gender, race, ancestry, marital status, education, date of
birth, place of birth, disabilities, work information, military service, language
spoken at home, housing information, and school enrollment.Not all questions are repeated each census year. For example, 100 percent of
the population was asked about their marital status in 1990; in 2000, it was only
asked on a sample basis. According to the analysis of the 2000 U.S. information,
on April 1, 2000, the population of the United States stood at 281,421,906.