THE ROLE OF POPULATION-SIZE IN THE DETERMINATION AND PREDICTION OF POPULATION FORECAST ERRORS - AN EVALUATION USING CONFIDENCE-INTERVALS FOR SUBCOUNTY AREAS

Producers of population forecasts acknowledge the uncertainty inherent in trying to predict the future and should warn about the likely erro r of their forecasts. Confidence intervals represent one way of quanti fying population forecast error. Most of the work in this area relates to national forecasts; although, confidence intervals have been devel oped for state and county forecasts. Studies have examined subcounty f orecast error, however, they only measured point estimates of error. T his paper describes a technique for making subcounty population foreca sts and for generating confidence intervals around their forecast erro r. It also develops statistical equations for calculating point estima tes and confidence intervals for areas with different population sizes . A non-linear, inverse relationship between population size and forec ast accuracy was found and we demonstrate the ability to accurately pr edict average forecast error and confidence intervals based on this re lationship.