Improving population estimates with the use of dummy variables

a The ratio correlation method of estimating county population may be improved with the use of dummy variables and stratification to represent county “type.” Unsatisfactory results were derived when the ratio correlation technique was applied to West Virginia counties using only such conventional symptomatic indicators as births, deaths, non-agricultural employment, and automobile registrations, probably due to the relatively unique absolute population decrease 1950–1960 that occurred in many counties. To improve the predictive power of the technique: counties were stratified along the lines recently suggested by Rosenberg; dummy variables were introduced to represent such county characteristics as region or rate of development; and stratification and dummy variables were combined in a single test. The average 1960 estimating error for the 55 counties was reduced from 4.6 to 2.3 percent when dummy variables and stratification were used to supplement the conventional indicators.