I have found research suggesting a number of biases vis-à-vis employee evaluations; often implicit in nature. Comments are always welcome, however, journals, critiques or lit reviews are what I am looking for.
1) I would combine them with 360 degree reviews. So, let the employees rate their superiors, too.
2) Keep the analysis seperate from the rest of the hierarchy.
3) Ask clear questions, do not let them just rate personal traits.
4) Make sure there is a follow-up process.
5) Employess should know their scores. Make sure there are ways to voice your complaint about wrong scores. Superior scores do not have to be open, as a) effect of single votes should be spilled by more people rating the superior's work, and b) even if a major percentage of the employees "underrates" a superior, that could be a very important sign of organizational / personal weaknesses.
6) You should NEVER directly combine those ratings with financial incentives company-wide. Different ratings for people in one department may be a sign of different performance, but different ratings for people in different departments, could just reflect varying levels of realism by the superiors, etc.
As expert in Performance Management and specially Key Performance Indicators. i would prefer to have Performance/Competencies Appraisal where 75% based on KPIs and 25% based on Competencies through performance review questions on a scale from 1 to 5 and to be reviewed on quarterly basis to give 3 opportunities for employees to improve and get better performance and results.