[KaeseEs]

The 10x figure is pseudoknowledge - something we "all know" that isn't actually true (or that at least we have no good reason to believe to be true), cf. http://vimeo.com/9270320 . In brief: the study that it is ultimately derived from had a tiny sample size (on the order of 30, to wit), and for several reasons the experimental design would have invalidated its results outside the very narrow original focus of the study (which was the relative productivity of batch processing vs. interactive processing on the computing systems of 1968) even if the sample size had been larger.

[JoeAltmaier]

The 10X figure is true. My study is 30 years of working with a wide variety of people in startup environments. Adding some people makes a project later. Others can manage a whole project alone (if they are LEFT alone).