Marketing Papers

Document Type

Book Chapter

Date of this Version

6-17-2001

Comments

Postprint version. Published in J. S. Armstrong (ed.), Principles of forecasting: a handbook for researchers and practitioners, Kluwer Academic Publishing, 2001, pages 417-439. The author asserts his/her right to include this information in ScholarlyCommons@Penn.

Abstract

To improve forecasting accuracy, combine forecasts derived from methods that differ substantially and draw from different sources of information. When feasible, use five or more methods. Use formal procedures to combine forecasts: An equal-weights rule offers a reasonable starting point, and a trimmed mean is desirable if you combine forecasts resulting from five or more methods. Use different weights if you have good domain knowledge or information on which method should be most accurate. Combining forecasts is especially useful when you are uncertain about the situation, uncertain about which method is most accurate, and when you want to avoid large errors. Compared with errors of the typical individual forecast, combining reduces errors. In 30 empirical comparisons, the reduction in ex ante errors for equally weighted combined forecasts averaged about 12.5% and ranged from 3 to 24 percent. Under ideal conditions, combined forecasts were sometimes more accurate than their most accurate components.

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Date Posted: 18 August 2006