ABSTRACT
Future demographic trends are inherently uncertain, and the further one goes into the future, the greater the uncertainty. On the other hand, few social and economic trends are as stable as population trends. No social scientist would challenge the statement that the percentage increase of the world population over the next five years can be more accurately projected than changes in unemployment rates, trade balances, or stock markets. Because of the great inertia of population trends, long term and short term mean different things for demographic and economic forecasts, but in all forecasts uncertainty is assumed to increase with the time horizon because of the greater probability of structural changes.
