Investigation of the Effects of Input Uncertainty on Population Forecasting

Cohort-component models have been used for many years to project future populations under a variety of scenarios. However, little work has been carried out on the effects of uncertainty in the model inputs on projection outcomes. The paper investigates these effects using a projection model for 12 European Community countries and 71 regions. Scenarios for fertility, mortality, extra-European Community migration, inter-country and inter-region migration drive the projections. The projection inputs are based on past data and expert opinion. The projection model program was modified to run on a parallel computer, which allowed thousands of model runs to be implemented, randomly perturbing all or some of the inputs. The simulation of input uncertainty allows error bounds to be placed on projection outputs. The results for individual inputs show how important is their contribution to output uncertainty. The analysis concludes with an evaluation of the approach used to handle uncertainty and makes suggestions for improvements and further experimentation.