>I can assure you that this is not easy. The SEL has been collecting human >effort data, program size data, error rates, and many other metrics for over >two decades. >... >What you're left with is a situation where only many experiments over time >can be used to arrive at statistically valid results. We'll take results at the 50% confidence level. ;) Seriously, it may take hundreds of years to get enough data to prove, at the 99% level and without a shadow of a doubt, that X is true. But even knowing that X is more likely true than not, is *useful* information. While we wait for certainty, people *are* making decisions that are more likely bad than good, based on their conclusions, statistically valid at *very* low confidence, from single circumstance anecdotes.