Getting Beta with Statistical PERT
Recently, a PMO director and I were having a working lunch together where he shared his frustration with his project teams, who were regularly delivering their projects later than scheduled. “I don’t understand why this is happening,” he confessed. “It seems like every project we plan takes longer than we expect.”
“Tell me about your approach to estimating projects,” I asked him.
“We do bottom-up estimating for our federal contracts,” he began. “I ask project team members to estimate how long each of their respective tasks will most likely take to complete, and they do that. Then I ask them how confident they are in their estimates, so I know how much buffer to add to the schedule.”
“And how confident are they?” I asked.
“They’ll say things like, ‘We’re 90% confident we can get those tasks done by our estimates,’” said the PMO director, who is also a good friend of mine. “And even though they’re 90% sure of their estimates, I’ll still add a little extra time in the project schedule, but no matter how much reserve I add, it’s never enough to finish our projects on time. I have great project managers who do a good job monitoring and controlling each project, but it doesn’t take long before they start reporting that some of
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