Why do the rates change for past years?
The rates change because the population estimates used the denominators in the rate calculations change. The population estimates used as denominators change in order to provide the most recently available best estimate. In the years following the decennial census, the Census Bureau annually produces a set of estimates containing estimates of the current year population and revised estimates of the population for previous years. Each set of estimates is referred to as a postcensal series. reference Description of the 1990-based Postcensal Population Estimates. See also Population Revisions. Note: a different 1991 data series is cited in the CMF 1998 documentation than is cited in the CMF 1995 documentation.
