Dear Preeti,
In addition to what other members have contributed I wish to share my views
As you have not mentioned what is the nature of job these unskilled workers are performing, I have assumed that they are performing the job of helpers (moving materials, packing, loading and unloading etc). In such cases there will not be a wider scope to appraise them. As Mr.Bhatia has rightly suggested you can go by only subjective appraisal and there will not be any objective appraisal.
On the other hand if these workers are also performing the job what your regular workers are doing then the scope widens. In such a case in my opinion you can follow the steps below
1) Identify all the skills available in the company and categorise them department wise.
2) Categorise these departmentwise skills in the ascending order (the least skill to the most complicated skill)
3) Prepare a training plan for these unskilled workers in consultation with the respective department heads.
4) Prepare a skill matrix plot the workers capabilities for each of the skills as - a) Don't know b) Knows but can't do (Lacks the physical strength, height, he can't be spared immediately as he is skilled in an alternate skill etc., ) c) Knows can do d) Knows can do and train
5) Once you have mapped this you know the current level of skills of these unskilled workers.
6) Prepare a training card that will contain the Name of the worker, identified skill, trainer, job number, Qty produced, Qty accepted and reasons for rejection and get is signed by the department supervisor and the worker himself. The card has to be filled up on every occasion the worker works in the respective skill.
7) At the end of each training period conduct an evalution for each skill acquired by him and plot his skill once again in the Skill matrix.
8) If you observe a shift in the skill category then you will be able to appraise his performance subjectively and the process will be transparent.The number of skills acquired/ enhancement of level in skills over the given period.
9) The skilled workers also earn appreciation in the appraisals considering the number of workers trained by them during a period.
10) Plotting their skills on a radar chart prior to the training period and after the training period will give you a visual picture of training acquired.
For Staff category in my opinion you can start with the objective rating method (Key performance areas/ Key result areas/ Key performance Indicators)
a) Set objectives, measurables, unit of measurement, frequency of appraisal and related scores.
b) The total score of the listed objectives should be equated to 100 for ease of calculation.
c) The employee needs to plot their achievements against objectives and scoring against each objective.
The employee's superior has to assess and guide the employee to excel in his performance. Of course you can also include subjective ratings for staff category such as innovation/ creativity in work, coherently working with superiors and peers, flexiblity in performance etc but each subjective rating has to be supported with examples for the appraisal period.
M.V.Kannan