While I'm not in HR, I'm jointly responsible for much of the technical hiring on my team. Today someone asked me how many people pass my original screening.
Answer: I'm assuming I don't see 90% of the resumes that cross our talent manager's desk. 90% of the resumes I do see don't make it to an initial phone interview. Of the 10% of candidates who do make it to a phone interview, only a quarter get to the full formal interview and the opportunity to get grilled by me and the engineers on my team.
I need to remember this when querying agents. The parallels are obvious. :-)