Soumik1570 is very right in saying, "appraisal has nothing to do with their education level."
Importance of Clarity in Performance Appraisal
What finally matters in any Performance Appraisal system is whether the individual concerned is clear about what is expected of him/her by the company and what parameters are being used to measure the performance. Quite often, it's the communication/understanding gap that mars the application of a Performance Appraisal system, however good the intent may be.
Given the education levels you speak of, it becomes even more important to keep in mind all the possibilities of understanding/communication gaps when the system goes into effect—and cover them beforehand. The key is to 'pre-empt' rather than to 'solve' when the situation arises.
On the Concept of Perfection
Coming to your line, "......I will be able to review perfectly," I recollect a quote: "Nothing is 'perfect,' however perfect it may be." Things can only get 'better' than they were earlier.
All the Best.
Regards,
TS