Criteria for Selecting a Suitable Method for Producing Post 2000 County Population Estimates in Illinois

Mohammed Shahidullah, Illinois Department of Public Health
Mark Flotow, Illinois Center for Health Statistics

Accuracy is the most important factor among the criteria in the selection of a method for producing population estimates. The following three sets of controlled county estimates and another set of uncontrolled estimates for the Administrative Records method were used for 2000: the Administrative Records method; the Ratio Correlation method; and an average of these. The 2000 estimates were adjusted for undercount. We compared performance of these methods with the performance of two naive models - i) "do nothing" by using the 1990 population as 2000 estimate and ii) "constant growth rate" by applying the growth rate between 1980 and 1990 to the 1990 population to obtain a 2000 estimate. We analyzed the data using mean absolute percent errors, mean algebraic percent errors and median absolute percent errors. Overall, the adjusted controlled Administrative Records method performed best.