IMA Journal of Management Mathematics Advance Access published online on December 1, 2007
IMA Journal of Management Mathematics, doi:10.1093/imaman/dpm032
| ||||||||||||||||||||||||||||||||||||||||||||||||
Hierarchical estimation as a basis for hierarchical forecasting

Department of Econometrics & Operations Research, Tilburg University, Warandelaan 2, PO Box 90153, 5000 LE Tilburg, The Netherlands
Email: l.w.g.strijbosch{at}uvt.nl
Received on 6 November 2006. Accepted on 29 October 2007.
In inventory management, hierarchical forecasting (HF) is a hot issue: families of items are formed for which total demand is forecasted; total forecast then is broken up to produce forecasts for the individual items. Since HF is a complicated procedure, analytical results are hard to obtain; consequently, most literature is based on simulations and case studies. This paper succeeds in following a more theoretical approach by simplifying the problem: we consider estimation instead of forecasting. So, from a random sample we estimate both the total demand and the fraction of this total that individual items take; multiplying these two quantities gives a new estimate of the individual demand. Then, our research question is: Can aggregation of items, followed by fractioning, lead to more accurate estimates of individual demand? We consider two simple situations that can be analysed fully theoretically. Thirdly, a more practical situation is investigated by means of simulation.
Keywords: hierarchical forecasting; aggregation; top-down approach