How sure are you about your estimate ?

As a project manager or as project team member, you need to make more than one estimate during the project.

  • How long will it take to complete ?
  • How much will it cost to realise ?
  • etc

Those who make the decision need to make sure their estimations are as accurate as possible, so how can you reflect “certainty” or “uncertainty” in your estimates?

I recently discovered an interesting tool developed by William W. Davis, MSPM, PMP, the Project Management Superhero , to get this done easily !


Estimating or guessing ? That’s the question.

Making an estimate might look like guess work, but when you have your facts and figures under control it will become a well calculated estimate instead of a “guesstimate”.

William W. Davis has bundled his expertise into a Microsoft Excel sheet or workbook. He combines the classic 3-point PERT (Project Evaluation and Review Technique) with some statistical mathematics.

Classic 3-point estimate

The classic PERT uses three values to calculate the estimate value :

  • minimum (MI),
  • most likely (ML),
  • maximum (MA)

The estimate value is then calculated as  : (MI + 4xML + MA) / 6

This is pure mathematical and thus not reflect any certainty or uncertainty about the 3 base values MI, ML, MA.

The SPERT method developed by William

The additional “S” does not come from SuperHero or SuperPower, but it relates to Statistics and Sensing.

Statistical PERT is a five-step process (but a SPERT template makes it only three steps). The five steps are:

  • Identify a minimum, most likely and maximum outcome for some uncertainty
  • Calculate the expected value using the PERT formula
  • Make a subjective judgment about how likely the most likely outcome really is
  • Calculate a standard deviation
  • Choose any probabilistic estimate that fits your desired risk level

SPERT templates do steps 2 and 4 for you, and Excel’s statistical functions in Step 5 make that a snap.


William offers all Statistical PERT example workbooks and templates, for free, to everyone.

Visit William’s website and download a free SPERT template.

He wants to remove barriers that keep people from exploring their own statistical superpowers, and he wants to encourage all businesspeople – especially project managers – to use statistics to quickly align stakeholder expectations and improve executive decision-making.

Go get it now !