You're making a broader point, which is fine and all. But your comments would be just as relevant if I said, "I pull out shared code into functions because that technique is useful to me". Your point is so broad that it's like a tautology. I really don't lose any sleep over the foundations of my approach to my work being unsupported by rigorous studies. You can feel free to be a science maximalist and run studies on whether pulling code out into functions is actually useful and all the rest of the approaches we've developed over the years. Meanwhile, I'll happily carry on doing stuff that I know is useful to me, like pulling out functions and using debuggers.