Chatter: Basic Manual Project Management – part 3: PERT Probability Calculations

  • Article

In Chatter: Basic Manual Project Management – Part 1: Cost Evaluation we looked at some of the basic cost evaluation techniques, in Chatter: Basic Manual Project Management – Part 2: PERT Techniques we explored the PERT techniques and in the end we mentioned that we may chat about the significance of the standard deviation in the next blog post, to calculate the probability of completing the project on time.Clipart Illustration of a Stressed White Employee Staring At Stacks Of Paperwork On A Desk, Trying To Figure Out Where They Can Put Their Computer Keyboard

Well, let’s conclude that topic for completeness.

image … extract from diagram in previous related post.

As part of the Chatter: Basic Manual Project Management – Part 2: PERT Techniques post, we determined that the standard deviation is 1.178 and for the sake of this post we assume that a stakeholder asks you what the probability is of you finishing this project on time in 14 (yeah), 16 (really) and in 20 days.

For this we dust off yet another calculation, namely z-value = (Target Date – Target Expected (te)) / standard deviation (s)

For …

  • 14 days we get a value of –1.698
  • 16 days we get a value of 0.00 and for
  • 20 days a value of 3.39.

Using a standard normal deviates table, which can be found on the Internet or in most stats books, we can determine the probability as follows:

 image   … by the way, I hand crafted this diagram. DO NOT se it for your project management planning … it is merely intended to illustrate the concept.

Therefore, based on the calculated z-values, we have a good chance of making the 16 days and a very good chance of making the 20 days.

That concludes my brief excursion through the basic project planning world.

Derek, please no frowning … I understand that the “Master of Project Management” has probably had a few nervous twitches while listening to a developer talk about project management topics :)