All staff must be appraised at least once a year. Do you agree or disagree or addition?

early and at the end of each major project. this may trigger more focus on tasks in hand.

the reasonable period to do the employee appraisal every six months in order to give the employee their weakness points to let them work on it.

the improvement will take time , so six months is enough to notice any improvement.

It's not fair to do it one time by year because the manager will give his evluation based on the employee achievements or bad performance in past few months.

I agree. But it is more better if we do it quarterly

This actually depends on the kind of business, the company's size. Some companies carry appraisal every six month and others every12 month. I prefer to have it every three month. It will keep things more smooth and working right. Employees need to know that the administration is aware of their progress and obstacles at work. This will make things more active, more interaction. This will help also hard working employees to stay ready to go forward. While employees with problems will find it  an opportunity to explain their issues.

I agree , but I think it need to be less than this , some organizations makes it weekly . 

Off course agree, but i think it's better to be twice a year

Agree but i think it would be in every3 month or six month

One year ok. I would say half yearly and quaterly.

I do agree.

Yes initially put the evaluation system should be twice a year to explain to him the use of the system and explain to managers and heads of departments on how to deal with the evaluation of performance and what are the mechanisms that must be met for the success of such a signature and the extent of distribution and natural axes and standards required to evaluate and year after two years at the discretion of the company can annual assessment work and to develop themes and standards for each function in addition to the goals of managers and heads of departments

We have to differentiate here between review meetings (interview) and final appraisal interview. For PA management, there should be performance review meeting at least every3 months in which the manager is review the progress of achieving the objectives and discussing the deviations in this progress and put solutions to get back to track. While at the end of the year, the rates are put and discussions are made for development plans etc.