Dear Rachel,
I apologize for not understanding your point initially. It is advisable to have appraisals from multiple sources, but this depends on the performance appraisal (PA) history within your organization. If your organization has a traditional PA system, it may be challenging for appraisees to adapt to a new multi-sourced system. Careful implementation is crucial. Each appraisee should be educated about the new system and be convinced of its benefits.
My suggestion is to gradually increase the sources involved. For example, you could start with peers, then gradually introduce feedback from subordinates, customers, and others.
Appraisees need to be open and proactive in receiving feedback from various sources. It should be taken constructively to avoid negatively impacting their mindset.
I hope this information is helpful to you.
Shradha