There's a simple method for software estimates that has worded well for me in practice. Imagine how long it should take if all goes smoothly, then multiply by pi.
By "worked well" I mean that x3 is the "about right" factor. As software engineers we tend to be optimisitic and so when I think "it'll take about a week", that's assuming no unforseen complications. I'm afraid I haven't conducted a detailed a statisical analysis, however. The pi method is in truth just a joke between myself and a former project manager. There's nothing magic about pi exactly. I imagine each person ought really to come up with their own mental multiplier based on their own tendency to underestimate. But 3 isn't a bad starting point for iteration.
I guess I'm asking what "about right" means. Does it mean you finish faster than that number 50 % of the time? 90 % of the time? No statistics necessary, just your gut feel.
Ah, good question. First instinct says 'success' should be statistically 50% each way. Right in the middle of the bell curve.
But on second thought, being behind estimate half the time would be pretty sucky. So I'd like to bring the peak of the curve onto the early side of the line.
I guess ultimately it depends on the question being asked of the estimator & the implied confidence interval.
