Actually the number from my old software engineering class is on the order of 36:1 in productivity from the most to least productive members of a team.
"P2. Good programmers are up to 30 times better than mediocre programmers, according to "individual differences" research. Given that their pay is never commensurate, they are the biggest bargains in the software field."
He also has a wonderful published book, "Facts and Fallacies of Software Engineering"
There were a number of problems with the quality of the individual differences research. I would not trust that particular number.
Another frequently cited source that was methodologically much better is the fact that 10 to 1 productivity differences are common even across small groups of programmers. Tom DeMarco and Timothy Lister performed this research and cited it in Peopleware. The two illuminating facts they also discovered at the same time were that the best predictor of programmer performance was the performance of other programmers at the same company, and that much of the productivity difference could be accounted for from differences in environment. (Sufficient office space, quiet office space, low interruption rates, etc.)
I would trust that number a lot more. And I would strongly recommend that anyone who is interested in it read Peopleware to get some ideas about how they can improve productivity.
