A New Short-Term County Population Projection Method 1

Abstract

This paper proposes a new method for short-term county population projections. It is based on a modification of the ratio-correlation method of population estimation. The modified ratio-correlation method can produce projections with a high potential for accuracy without requiring substantial data and intensive intellectual labor inputs. Tests of accuracy are examined for the modified ratio-correlation method and two currently available alternatives using data from Washington state. The tests suggest that the new method performs well. Advantages of the modified ratio-correlation method are discussed, with particular attention given to the formal measurement of uncertainty. Forecast intervals are constructed and examined for the projections constructed for counties in Washington state. Given certain limitations, the forecast intervals appear to be robust in terms of providing accurate assessments of the precision associated with county population projections made using the modified ratio-correlation method.