One thing I don't recall seeing mentioned in these discussions is validity checking based on the different sources of ratings. If you're seeing widely varying

One thing I don't recall seeing mentioned in these discussions is validity checking based on the different sources of ratings. If you're seeing widely varying ratings of a single person that seems like it'd be a big red flag - if the boss says 1 or 2 but coworkers or reports average 3.5+ that's a situation that seems to cry out for further investigation. Similarly, if the boss says "4" but coworkers and reports average 1.5, there's probably also a serious problem. I'm sure investigating involves costs that companies don't want to incur, but if you have that kind of disconnect going on it may be cheaper to investigate and resolve it than to deal with the eventual fallout. I've seen the personal aftermath of bad bosses and work environments on people in the past, and it's really not pretty. If you're talking with someone about work and say "Mean Girls" and get a response of "Oh my god yes!" that's a pretty good indicator of a toxic work environment.