A simple and logical alternative for making PERT time estimates. (Program Evaluation and Review Technique): An article from: IIE Transactions
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ISBN / ASINB00096K0KA
ISBN-13978B00096K0K9
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This digital document is an article from IIE Transactions, published by Institute of Industrial Engineers, Inc. (IIE) on March 1, 1996. The length of the article is 8110 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser.
From the author: The two standard steps for estimating PERT times are: Step 1, estimate a, m, and b; and Step 2, use the 'classical' formulae [Mu] = (a + 4m + b)/6 and [Sigma] = (b - a)/6. We review the shortcomings of the textbook definitions of a, m and b; we also review the inconsistency of Step 1 with the literature on probability elicitation. A 5- or 7-fractile alternative is then proposed and justified for Step 1. Next, we develop simple but very accurate formulae for computing [Mu] and [Sigma] with the fractiles estimated in our Step 1. For contrast, we also show that the classical PERT formulae are very inaccurate, even for the very restricted subset of beta distributions for which the formulae are supposedly applicable. Our overall purpose is to combine earlier findings with some new results to argue that: (i) the classical PERT formulae are both illogical and inaccurate, so we should not continue to teach and use them; and (ii) simple and more logical alternatives are available.
Citation Details
Title: A simple and logical alternative for making PERT time estimates. (Program Evaluation and Review Technique)
Author: Amy Hing-Ling Lau
Publication:IIE Transactions (Refereed)
Date: March 1, 1996
Publisher: Institute of Industrial Engineers, Inc. (IIE)
Volume: v28 Issue: n3 Page: p183(10)
Distributed by Thomson Gale
From the author: The two standard steps for estimating PERT times are: Step 1, estimate a, m, and b; and Step 2, use the 'classical' formulae [Mu] = (a + 4m + b)/6 and [Sigma] = (b - a)/6. We review the shortcomings of the textbook definitions of a, m and b; we also review the inconsistency of Step 1 with the literature on probability elicitation. A 5- or 7-fractile alternative is then proposed and justified for Step 1. Next, we develop simple but very accurate formulae for computing [Mu] and [Sigma] with the fractiles estimated in our Step 1. For contrast, we also show that the classical PERT formulae are very inaccurate, even for the very restricted subset of beta distributions for which the formulae are supposedly applicable. Our overall purpose is to combine earlier findings with some new results to argue that: (i) the classical PERT formulae are both illogical and inaccurate, so we should not continue to teach and use them; and (ii) simple and more logical alternatives are available.
Citation Details
Title: A simple and logical alternative for making PERT time estimates. (Program Evaluation and Review Technique)
Author: Amy Hing-Ling Lau
Publication:IIE Transactions (Refereed)
Date: March 1, 1996
Publisher: Institute of Industrial Engineers, Inc. (IIE)
Volume: v28 Issue: n3 Page: p183(10)
Distributed by Thomson Gale
