Age-specific demographic modeling and forecasting: Rolling window, expanding window, or both?

Rolling and expanding windows are widely used in age-specific demographic modeling and forecasting. Building on these approaches, we propose a simple combination method that assigns equal weight to the forecasts from both schemes. Our focus is on evaluating and comparing the forecast accuracy of the two window types in modeling age-specific mortality and fertility. Based on the multi-country comparison, the superior performance of one method often persists across different forecast horizons. In the absence of prior information, our combined approach offers a robust and practical alternative.