I worked at a rather largish virtualisation company which uses the "Nine Box" performance review process. The idea is that you get two scores, your _public_ score which is told to you about your performance, and then a _private_ score which is surreptitiously given by your manager about your potential to get promotions.
Managers are then given a quota of how many people should be put in which box, and get hammered if they give too many people good reviews. The "secret" score is directly tied to your compensation, so basically your manager could be completely screwing you and you would have absolutely no indication.
My suspicion would be they use plausible deniability. "We're not giving out great raises this year". Which is technically not a lie, I suppose. They're not giving out a great raise _to you_.
Managers are then given a quota of how many people should be put in which box, and get hammered if they give too many people good reviews. The "secret" score is directly tied to your compensation, so basically your manager could be completely screwing you and you would have absolutely no indication.