This assumes that a job opening has a perfect distribution of applicants. Let's take another hypothetical; Bob's factory posts machinist ads on Craigslist. CL

This assumes that a job opening has a perfect distribution of applicants. Let's take another hypothetical; Bob's factory posts machinist ads on Craigslist. CL turns out to send Bob 90% males and 10% females. Bob decides to try to increase the number of females he hires, and advertises on a second site. Turns out this site is viewed by a higher percentage of females, and thus his number of female applicants increases, and the bar for hiring stays the same.