By superiors, third parties, customers, peers, subordinates, self-appraisals
Includes information from many possible angles
Any one of these is going to be biased for a number of reasons
If you take in all of these though, and find a way to reconcile, you have more measurements on how to find performance
Disadvantage - all perspectives only see components of performance - very rarely are scores consistent between raters (not a holistic view)
Many different data points, different viewpoints but no one has all of the information
Use it to triangulate between different assessment items