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Aggregating Subjective Forecasts: Some Empirical Results

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  • Alison Hubbard Ashton

    (Graduate School of Business Administration, New York University, New York, New York 10006)

  • Robert H. Ashton

    (Graduate School of Business Administration, New York University, New York, New York 10006)

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    Abstract

    The impact on forecast accuracy of aggregating the subjective forecasts of up to 13 individuals was examined for five forecast weighting methods---equal weighting, two ex post methods that took advantage of prior information about the individuals' relative accuracy, and two ex ante methods based on objective and subjective assessments of relative accuracy. The individuals were executives, managers and sales personnel employed by Time. Inc., and the variable forecasted was the number of advertising pages sold annually by Time magazine over a 14-year period. The results show that both the average forecast error and the variance of the error decrease as additional individuals' forecasts are included in the aggregate. Only two to five individuals' forecasts must be included to achieve much of the total improvement available from combining all 13 forecasts. Three of the differential weighting methods produced more accurate forecasts than equal weighting, but the magnitude of the improvement was small. Implications for realistic forecasting situations are discussed, as are conditions under which the use of aggregates seems attractive.

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    File URL: http://dx.doi.org/10.1287/mnsc.31.12.1499
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    Bibliographic Info

    Article provided by INFORMS in its journal Management Science.

    Volume (Year): 31 (1985)
    Issue (Month): 12 (December)
    Pages: 1499-1508

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    Handle: RePEc:inm:ormnsc:v:31:y:1985:i:12:p:1499-1508

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    Keywords: forecasting: applications;

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    Cited by:
    1. Ramnath, Sundaresh & Rock, Steve & Shane, Philip, 2005. "Value Line and I/B/E/S earnings forecasts," International Journal of Forecasting, Elsevier, vol. 21(1), pages 185-198.
    2. Hurley, W. J. & Lior, D. U., 2002. "Combining expert judgment: On the performance of trimmed mean vote aggregation procedures in the presence of strategic voting," European Journal of Operational Research, Elsevier, vol. 140(1), pages 142-147, July.
    3. Osherson, Daniel & Vardi, Moshe Y., 2006. "Aggregating disparate estimates of chance," Games and Economic Behavior, Elsevier, vol. 56(1), pages 148-173, July.
    4. Ilan Yaniv, 2005. "Receiving Other People's Advice: Influence and Benefit," Discussion Paper Series dp405, The Center for the Study of Rationality, Hebrew University, Jerusalem.
    5. Fischer, Ilan & Harvey, Nigel, 1999. "Combining forecasts: What information do judges need to outperform the simple average?," International Journal of Forecasting, Elsevier, vol. 15(3), pages 227-246, July.
    6. Sanders, N. R., 1997. "The impact of task properties feedback on time series judgmental forecasting tasks," Omega, Elsevier, vol. 25(2), pages 135-144, April.
    7. Scheibehenne, Benjamin & Broder, Arndt, 2007. "Predicting Wimbledon 2005 tennis results by mere player name recognition," International Journal of Forecasting, Elsevier, vol. 23(3), pages 415-426.
    8. Yaniv, Ilan, 2004. "Receiving other people's advice: Influence and benefit," Organizational Behavior and Human Decision Processes, Elsevier, vol. 93(1), pages 1-13, January.
    9. JS Armstrong, 2004. "Forecasting for Environmental Decision Making," General Economics and Teaching 0412023, EconWPA.
    10. Yaniv, Ilan & Kleinberger, Eli, 2000. "Advice Taking in Decision Making: Egocentric Discounting and Reputation Formation," Organizational Behavior and Human Decision Processes, Elsevier, vol. 83(2), pages 260-281, November.
    11. Yaniv, Ilan, 1997. "Weighting and Trimming: Heuristics for Aggregating Judgments under Uncertainty," Organizational Behavior and Human Decision Processes, Elsevier, vol. 69(3), pages 237-249, March.
    12. Lubecke, Thomas H. & Nam, Kyung Doo & Markland, Robert E. & Kwok, Chuck C. Y., 1998. "Combining foreign exchange rate forecasts using neural networks," Global Finance Journal, Elsevier, vol. 9(1), pages 5-27.
    13. Budescu, David V. & Rantilla, Adrian K. & Yu, Hsiu-Ting & Karelitz, Tzur M., 2003. "The effects of asymmetry among advisors on the aggregation of their opinions," Organizational Behavior and Human Decision Processes, Elsevier, vol. 90(1), pages 178-194, January.
    14. J. S. Armstrong & R. Brodie, 2005. "Forecasting for Marketing," General Economics and Teaching 0502018, EconWPA.
    15. Yaniv, Ilan & Milyavsky, Maxim, 2007. "Using advice from multiple sources to revise and improve judgments," Organizational Behavior and Human Decision Processes, Elsevier, vol. 103(1), pages 104-120, May.

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