Determining when to update the weights in combined forecasts for product demand – an application of the CUSUM technique

Combining forecasts merges several separate sets of forecasts to form a better composite forecast. There has been much published work on how to find the optimal combining weights. Several authors have suggested that changing the weights from time to time would be better than using fixed weights (FW). The unresolved problem is when to change the weights, on a regular basis or otherwise. The aim of this paper is to use the techniques of quality control to decide when we need to change the combining weights. An efficient and simple method to control the weights of the combined forecast is proposed and shown to perform better than one based on FW.