Can't argue that O&P estimates aren't tainted. My comment was based on what I've seen reviewing hundreds of projects in large enterprises. Most engineering projects rigorously estimate as a matter of course. Internal business projects often rely on educated guesses based on experience. It's hard enough to get them to document the basis for their estimates, quantitative or qualitative, much less to develop three different estimates and the basis for each as PERT demands. Chock it up to different schools of thought. We expect business managers to be strategic, big picture people.
PERT can help you come up with a more likely best guess. My point is that if you aren't going to put the effort into estimating O&P it won't help and may even mislead.
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