If you're going to ask that, you should tell us which studies you used to select the other techniques you use.

(It turns out that there are, tons actually, but software engineering a difficult topic to study and I wouldn't draw any conclusions from them. The vast majority of controlled software engineering studies I've seen are conducted on students using problems of trivial scope. The uncontrolled ones aren't much better. Basic questions like "what do you mean by productivity" have yet to be answered well.)