Appraisal:What's appraisal method to use for produced company?

Dear all,

If your company have over 2000 employeer and you want to apply the appraisal, what's the appraisal method to use for your company?

Because of we haven't effort to do that for 2000 employee per months.

Please help me to give some solution.

Thanks you so much

Huyen Nguyen