Huh. That there's pretty rude, in't?

Dunning-Kruger is a sad thing, and pretty much incurable.

Cheeri-O.

Steve the Bajan

Dennis wrote: "...I would use the trigen if (big if) I thought the ranges given were understating the risk - my respondents were risk accepting, giving optimistic estimates.  I would use triangle if I thought they fully understood/appreicated the risk(s)."

That's sort of the big problem with Monte Carlo risk simulation packages, isn't it? Nobody knows what the objectively "correct" number is, so if we run it on one default and don't like the answer, we tweak it until we get the answer we wanted all along. In other words, we decide what number we want and then use pseudo-science to justify our gut instincts. it's the classic example of "garbage in, gospel out".

Monte Carlo systems can provide valuable information if:

1. There is good historical data showing activity durations and effort on similar work, and:
2. We map the distribution curve to each specific activity.
3. They either include no lags or, as with Spider Project, the lags can be volume lags that can be varied according to the simulated distribution.

But almost no one does any of that -- it’s too much work. Instead, they pluck three estimates out of thin air and then they run the simulation using a default, And if they don't like the results fromthat default, they use another one. And, as Dennis suggests, the whole purpose is to satisfy a customer who knows nothing about the process but is impressed when told: "It must be accurate -- it came out of a computah!"

Fraternally in project management,

Steve the Bajan

Claire:

For me, the difference is whether or not my respondents are risk adverse, risk accepting, or neutral.  Of the two possible distrubutions you cite, I would use the trigen if (big if) I thought the ranges given were understating the risk - my respondents were risk accepting, giving optimistic estimates.  I would use triangle if I thought they fully understood/appreicated the risk(s).  Since it is relatively easy to change the risk distributions in the layout, I might run both just for grins. I would run BetaPert to model the risk adverse case.

Hope this helps.