| The problem is noise. Say you want to take 10% at each round. You have to do this three times to get 100 people, and then another round to get the top 30. If you tighten the criterion, noise matters more, so you will drop your actual best candidates, since people need a high skill+noise. But if you try to keep the unlucky "good" candidates by having a wider band, you pay more. Also, if you are successful at finding the best candidates in a batch, noise matters even more the next round. I've been thinking about how to vizualize this. I have it in my mind and I'll try to describe it. You plot a bunch of points with S, N for each candidate. They are independent, so a scatter plot looks like a 2D gaussian. Lets say skill is vertical, and noise is horizontal. You want to find the 30 highest points, but you aren't allowed to just look on the scatter plot and select the top points. You have to draw a line S + N = c, and choose the person with the highest c. Basically sliding a ruler out that crosses the S and N axes as far away from the origin as possible. Observation: if N is high (wider distribution) compared to S, you just get the luckiest people. If S is high compared to N, you just get the most skillful. |
If you want to reduce noise, the way to do it is to have more independent measurements (interviewers), not to stop interviewing early.
The good news is that there’s no such actual thing as “best” in this situation and people have many dimensions, they can’t be ranked perfectly, but they can still be ranked approximately. We also don’t need to get the exact 30 people out of 100k people with infinite precision, we will get an amazing set if we can take a random sample of the top 1000 candidates out of 100k candidates. Having 100k candidates gives us the opportunity to end up with a selection from the top 1%, say, whereas if the number of applications was 40 people for 30 jobs, you might be stuck accepting people who are below average.