A number of my boss's reports had landed in the achieves category for all of 2014, but nonetheless received a communication from HR this past April that they were in the bottom 5% of the company for 2014 and at risk for termination if their performance did not improve. This surprised my boss and the reports.
Obviously if you're in the bottom 5% you're well below average. The question is how you can consistently be ranked in the middle category yet nonetheless be in the bottom 5%. That would seem to make the quarterly ratings a rather pointless exercise for communicating to employees what their ongoing performance is.
This is not true.
If the bottom 50% are all very close in absolute performance, you get exactly the situation described, which is exactly the steady state of the process you desribe. The process is working too well.
I told you just three days ago that if you wouldn't or couldn't stop doing this, I would ban your account [1]. This comes after more warnings, reminders, cajolings, and please-dont's than anyone has received in the history of HN by a long shot. It's painfully evident that you won't or can't stop, and it's time we applied the rules equally.
1. https://news.ycombinator.com/item?id=9994684
Edit: the parent comment was killed by user flags. We didn't delete it or moderate it.
The reasons are the ones I gave and have given many times.