>Enough for what? Why not? Let me throw out some made up numbers as an example. Company X hires 100 people out of 500 applicants. If only 30% of them perform

>Enough for what? Why not? Let me throw out some made up numbers as an example. Company X hires 100 people out of 500 applicants. If only 30% of them perform well, you might argue the interview process is rubbish. However, if you can test and show that of the "un-hired" 400 only 5% would perform well, then clearly the interview process is better than picking at random. This is why just looking at hired performance is not indicative of whether the process works - because the task was not just to predict good performers but to predict a better rate of good performers than a random sample of applicants.