Question from Oliver Lehmann (www.oliverlehmann.com)

Submitted by Hylton on Sun, 07/08/2012 - 18:59

 

Assuming ±3 sigma precision level for each estimate, what is the standard deviation of the allover path?

Answer for this question comes up as: Standard deviation all over the path is 5.2 days. 

In my opinion answer is 4.69.

Sum of variance[(P-O)/6] ^2=  4+1+4+9+4 = 22

Standard Deviation =sq.root 22 = 4.69

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diba_perfect

Sun, 07/08/2012 - 19:11

 Hylton,

standard deviation of Act. E = (35-17)/6 = 3; thus variance = 9; so sum of variance(path) = 27; standard deviation of path = sq. rt.(27) = 5.2

the last figure in your variance summation is = 4..why?

Hylton

Sun, 07/08/2012 - 20:00

 Thank you very much Diba! Thank you for highlighting my mistake!  Got it! 

 

sspawar

Mon, 07/09/2012 - 00:24

http://www.isixsigma.com/methodology/project-management/better-project-m...
http://www.interventions.org/pertcpm.html

Hylton

Mon, 07/09/2012 - 01:05

 Thanks for these great references sspawar! In the following, what is St?  Is it standard deviation? How is calculated?

Now, although the project is estimated to be completed within 28 weeks (te=28) our Project Director would like to know what is the probability that the project might be completed within 25 weeks (i.e. Due Date or D=25).

For this calculation, we use the formula for calculating Z, the number of standard deviations that D is away from te.

sspawar

Mon, 07/09/2012 - 01:27

t = 1, 2, 3 diff sd

Hylton

Mon, 07/09/2012 - 01:51

 Thanks a million!