(FWIW, I would pay much more attention to individual performance differences if I were hiring for my own startup than I would when interviewing for Google. But I thought the context of this discussion was organizations large enough for gender quotas to matter, i.e. the Microsofts and Googles of this world. If it were my own startup, I'd try to hire from the population I've personally worked with, avoiding this whole discussion anyway. And I have never worked in an organization with a hiring quota - the companies I've worked for will all take you if you meet the hiring bar, and hold cash in reserve so they can scoop up a suitably-qualified employee if one presents herself. For that matter, I've been given offers at several places that were "not hiring", so I'm guessing quotas are just guidelines in many other places as well.)