4 ms·
No, there is no justification, they just picked that because it has finite limits. They say it's a Beta distribution. PERT was invented by the US Navy but thes
by SixSigma 11y ago
No, there is no justification, they just picked that because it has finite limits. They say it's a Beta distribution.
PERT was invented by the US Navy but these days the DoD recommends not using it but just use normal Critical Path Analysis instead where you just estimate a single time - hard enough on it's on without having to do it three times.
- jacques_chester 11y agoRight, 3-points are tedious to do by hand. That's why I began working on a tool. I figured if it's easy enough, people would actually do it.
- SixSigma 11y agoAnd it also assumes that the optimal is just as likely as the pessimistic. As anyone who has ever planned anything knows, more things can conspire to introduce delay than work out just right enough to make it take less than you excepted.
- jacques_chester 11y agoRight, and there's lots of literature jumping on that and trying to repair it. Yet the original formula outperforms single point estimates. But as I said elsewhere in this thread, my suspicion is that the unpacking effect dominates the "improvement" that's observed and that the particular formula is largely secondary.
- SixSigma 11y agoOh yes, you did say that, sorry. I only responded to your first point and then remembered the second myself. PERT is taught as a time based planning tool but it also has a earned value element. The tools for that have moved on too. https://en.wikipedia.org/wiki/Earned_value_management https://en.wikipedia.org/wiki/Earned_value_management I suppose the unpacking effect does make more sense though, over CPA. "How long will it take?" "6-8 weeks" So what do you put in CPA - 6, 7, 8 ? PERT says 7.