# Calculating Variance of Activity the PMP way

When I was studying for the PMP exam, a few years ago, I remember memorizing a group of formulas. One of those was the “Variance of Activity.” At this point, don’t remember if it was even referenced in the exam. There were no direct questions asking “what is the formula for…” On my exam, I remember having numerous questions resulting from schedule variance calculations and cost variance calculations. To my surprise, I went searching for the Variance of Activity formula in the PMBOK (4th Edition) and I can’t find it! So as not to lead people astray when giving PMP study advice, I’m now researching each formula I was once told to memorize. I’m very surprised PMI didn’t save us a lot of trouble and list known formulas in the back of the PMBOK.

## 10 Replies to “Calculating Variance of Activity the PMP way”

Interesting observation Derek…I noticed the same and actually found it useful to read Rita Mulcahy’s book chapter for chapter for such gaps.

Poonam S Bhogal

Poonam, thank you for adding your recommendation. When people are prepping for the PMP exam, I always recommend they read Rita Mulcahy’s book. To the point of the formula, I do know that it’s a statistical formula. It’s so common, you can find it as a canned formula in Excel. I just come from the approach, when in doubt, put it in the book.

Thanks Derek. The formula has typing error in Rita Mulcahy’s book. Rao

Wow, of all the typing errors to go to print, a formula? Ouch! Thank you, Rao, for pointing that out.

I’m reading Rita’s book and I see the formula but I don’t see any explanation of what activity variance means or what it is used for.

Chris, it’s a quantifiable deviation from an expected baseline or estimate. Honestly, your “best guess” on an estimate may be just as accurate as a estimated calculated with activity variance. But, when it comes to the PMP, memorize it! See how it interacts with the other formulas you’ll also have to memorize.

If optimistic time

for an activity is 5 days, estimated time to complete the activity 85 and most

likely time 10 days. What is the variance of the activity?

The variance of the activity is still calculated by subtracting the optimistic time from the pessimistic time, dividing the difference by six and then squaring the outcome.

Greetings

Can you help me? Can you take me through the steps of calculating a path variance if you have been given only the activity duration? Am struggling to first calculate the estimates for each activity, since I don’t know how to come up with the most likely pessimistic and optimistic times if am given only the activity duration

Melusi,

If you have the activity durations, calculate the standard deviation. Path variance is actually just Standard Deviation ^2