On Estimating a De Facto Population and Its Components

This paper deals with estimating a population that is largely defined by the fact that neither its size nor composition are readily accessible from census data in the U.S. and the other countries that use the De Jure concept of population. The population in question is that of de Facto population, which is the concept of people enumerated, estimated, or forecasted where they are found rather than where they usually reside. Estimating this type of population as well as its components is an important, but not easy task. In an effort to develop this field of population estimation more fully, we provide an equation to define the De Facto population and an example of its use. We describe and discuss each of the components of this equation and also provide examples of estimates of its direct components and an implied component – the daytime population. Although we view a population impacted by a disaster as distinct from a De Facto population, we include a discussion of it here since many of the methods used to estimate a De Facto population are applicable.