Blackwell Reference Online

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Population projections and estimates constitute a core focus of demographic techniques. Both activities calculate the size and often the demographic characteristics of a given population in the absence of complete data such as might be available from a population census. Population projections and estimates play an important role in analysis of societal trends and in planning and policy decisions. Population projections and estimates are sometimes distinguished from each other by the statement that population estimates refer to current or past dates while population projections refer to future dates. A better distinction would be based on the time period of the input data relative to the output data. Population projections take the data on trends in population size and/or in the components of population change (births, deaths, and migration) and use mathematical models to extrapolate these trends into a time period not covered by the data. Usually, but not always, projections are done for some point in the future that is not only beyond the last date of the input data but also beyond the date that the projection is actually prepared. Population estimates relate to a past time period for which population counts are not available (such as the years after the most recent population census). In contrast to population projections, population estimates take advantage of actual measurements ... log in or subscribe to read full text