Help - Plot a normal curve for a PERT

[pmcleod]

I am a PM in Canada. I used to use this site almost daily but have not been back for a while. at the first sign on trouble ... this is the first place I thought of!

Attached is an Excel sheet that uses the PERT formula to plot out how long it will take to do project work. Based on 3 points it plots an expected value from which you can determine a standard deviation to work out the rage of days work will take with increasing or decreasing probability.

I am trying to plot the probability of completion as a % on one axis and the days to complete the work plotted out in either direction from the expected days. A normal, normal curve.

Based on these statically ideas:

• Work will be completed within plus or minus 1SD of Expected Value 68.3% of the time.
• 2SD of Expected Value 95.5% of the time.
• 3SD of Expected Value 99.7% of the time.

Obliviously the further out we get on the probability distribution curve, the wider the range – but the higher the confidence.

ANYWAY .... I CANTNOT for the life of me seem to figure out how to plot this using a scatter diagram.

PLEASE take a look at what I have done and let me know if you can help.

Thanks, in advance.

Perry McLeod, CBAP, PMP
Senior Professional Services Consultant
Davis + Henderson | Credit Solutions | Professional Services
276 King Street West, Suite 400, Toronto, ON, M5V 1J2
Office: +1 (416) 360-1777 (x3460)| Toll Free: +1 (866) 345-6449 | Mobile: +1 (416) 569-4651 | Fax: +1 (416) 360-8224
E-mail: perry.mcleod@dhltd.com | Web: www.dhltd.com

 

[chergh]

Change :

=NORMDIST(N1,$A$11,$A$13,FALSE)

to

=NORMDIST(N1,$A$11,$A$13,TRUE)

and then copy it down the rest of the column