Improved moment-estimation formulas using more than three subjective fractiles

Improved moment-estimation formulas using more than three subjective fractiles

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Article ID: iaor19991521
Country: United States
Volume: 44
Issue: 3
Start Page Number: 346
End Page Number: 351
Publication Date: Mar 1998
Journal: Management Science
Authors: , ,
Keywords: project management
Abstract:

PERT-type subjective estimations are used in many stochastic decision models to estimate the random variables' mean and standard deviation (s.d.). The approach is based on the beta-distribution assumption; also, most PERT-type formulas use only three estimated fractiles. We point out that: (i) it is desirable to consider a substantially richer set of distributions than the beta in developing PERT-type formulas; (ii) it may be beneficial to use more than three fractile-estimates in PERT-type formulas. We then develop formulas for estimating the mean and s.d. that are based on a substantially richer set of distributions than the beta and that use more than three estimated fractiles. These formulas perform better than the best currently-available formulas when the subjective distribution is not restricted to be beta.

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