Scheduling Project Tasks
By Jason Hecker
One of the biggest challenges Project Managers face is scheduling our projects – especially when we have tasks that cannot begin until other tasks are completed.
Effort vs. Duration
I usually know how long something will take me in terms of the effort required, but often a more urgent task or project will take priority over the time that I had originally scheduled for myself to work on a particular task. Not only does this delay the completion of my original task, but also the dependent tasks I had scheduled after it.
For example, I need to create the content for a custom Project Management course. The client wants me to include some additional material regarding effective project meetings and follow up.
Based on past experience, I know this task should only take me about 4 hours of effort – but my availability this week will most likely determine the duration (in calendar days) the actual activity will take.
Now if this mini-project didn’t have a hard deadline or due date, a schedule wouldn’t be that big of a deal. I could just get it done whenever I can carve out the time. But I do have a deadline, because the course needs to be delivered on a specific date.
I also have certain tasks (like create the PowerPoint slides and rehearse my presentation) that are dependent on me having the course materials complete. I can’t schedule those tasks if I don’t have my content finished.
Program Evaluation Review Technique
PERT is an acronym that stands for Program Evaluation Review Technique. Not to be confused with the shampoo that includes conditioner in the same bottle, PERT is an activity estimation technique developed by the US Navy’s Special Project Office. I use it to schedule project tasks that have a range of possible completion dates.
Basically, PERT works like this:
I first identify 3 estimates –
1) The most likely duration estimate (measured in calendar days) of how many days it will take me to complete this task (ML)
2) The best case scenario (BC), and
3) The worst case scenario (WC)
I usually estimate task duration (calendar days) rather than effort since I can rarely schedule all the effort hours together at the same time.
PERT In Action
I know that it should take me about four hours to create the custom course content, but I’ll probably have to do it over six days, as I can only devote about an hour a day to that task and I want to allow for some rework and editing. So my “Most Likely” PERT estimate is 6 days.
I then multiply that most likely estimate by 4. Since it’s my most likely scenario, I want to give it more weight than my other two estimates.
I then estimate my “Best Case” scenario. Assuming everything goes well and there’s not much rework or editing needed, I could hopefully get it done in 4 days.
Finally, my “Worst Case” scenario – If I can’t knock this out in 6 days, there’s a chance it could really get behind, as I’ll be in the classroom and on the road a lot after next week. Looking at my upcoming calendar, this could conceivably take me as long as 20 business days – an entire month!
I then take all three estimates (remembering to multiply my most likely estimate by 4) add them together, and then divide that number by 6.
(6x4)+4+20 = 48
48/6 = 8
*BC= Best Case
This gives me my PERT estimate – which comes to 8 days. This is what I’ll use for my task duration estimate. I’ll schedule the subsequent tasks (the PowerPoint and the rehearsal) to begin 8 days from now.
More Accurate Over Time
I have found PERT to be more consistently accurate over time. Is it always right? Of course not, as the nature of my work schedule is such that I don’t always know how long a particular activity will take. But for my task scheduling purposes, PERT helps me more accurately predict what the entire project duration will be by allowing me to account for days with and without interruptions, rework, and emergencies.
Try it for yourself with your next project and let me know how it works for you.