"4/6ths approximates 66.7%, which approximates 68%, which approximates the area under a normal distribution within one standard deviation of the mean."
"The reason why you multiply by 4 to get the Mean (and not 5, 6, 7, etc.) is because the number 4 is tied to the shape of the underlying probability curve."
"The cone of uncertainty uses the factor 4 for the beginning phase of the project."
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4 replies by Anish Abraham, Poonam Jain, Rami Kaibni, and VINAYAK KATKAR
Senior Projects Manager | Field & Marten AssociatesNew Westminster, British Columbia, Canada
Oct 30, 2018 6:19 PM
Replying to Sante Delle-Vergini, PhD
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I saw this explanation in a search:
"4/6ths approximates 66.7%, which approximates 68%, which approximates the area under a normal distribution within one standard deviation of the mean."
"The reason why you multiply by 4 to get the Mean (and not 5, 6, 7, etc.) is because the number 4 is tied to the shape of the underlying probability curve."
"The cone of uncertainty uses the factor 4 for the beginning phase of the project."
Interesting explanation Sante Saving Changes...
Sergio Luis ConteHelping to create solutions for everyone| Worldwide based OrganizationsBuenos Aires, Argentina
Poonam JainProject Manager| Morgan StanleyHicksville, Ny, United States
Oct 30, 2018 6:19 PM
Replying to Sante Delle-Vergini, PhD
...
I saw this explanation in a search:
"4/6ths approximates 66.7%, which approximates 68%, which approximates the area under a normal distribution within one standard deviation of the mean."
"The reason why you multiply by 4 to get the Mean (and not 5, 6, 7, etc.) is because the number 4 is tied to the shape of the underlying probability curve."
"The cone of uncertainty uses the factor 4 for the beginning phase of the project."
The beta distribution is essentially a bell curve of typical probability distribution that applies to many things. A distribution can be symmetrical, biased to the high end or low end, have very long "tails" at the ends, a tall skinny bell shape or a broad fat one, etc.
The simple algebraic formula using the high and low estimates at the ends, 4x the "most likely" estimate and dividing by 6 basically approximates the bell curve describing your estimates as 3 rectangles (small ones at the end and big one in the middle) and finds the average area to get a statistical "most likely" which takes into account where you think you'll be along with how much uncertainty you have on both the high and low sides. Saving Changes...
Anish AbrahamPrivacy Program Manager| University of WashingtonAuburn, Wa, United States
Oct 30, 2018 6:19 PM
Replying to Sante Delle-Vergini, PhD
...
I saw this explanation in a search:
"4/6ths approximates 66.7%, which approximates 68%, which approximates the area under a normal distribution within one standard deviation of the mean."
"The reason why you multiply by 4 to get the Mean (and not 5, 6, 7, etc.) is because the number 4 is tied to the shape of the underlying probability curve."
"The cone of uncertainty uses the factor 4 for the beginning phase of the project."
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