Managers commit mistakes while evaluating employees and their performance. Biases and judgment errors of various kinds may spoil the performance appraisal process. Bias here refers to inaccurate distortion of a measurement. These are:

1. First Impression (primacy effect): Raters form an overall impression about the ratee on the basis of some particluar characteristics of the ratee identified by them. The identified qualities and features may not provide adequate base for appraisal.

2. Halo Effect: The individual’s performance is completely appraised on the basis of a perceived positive quality, feature or trait. In other words this is the tendency to rate a man uniformly high or low in other traits if he is extra-ordinarily high or low in one particular trait. If a worker has few absences, his supervisor might give him a high rating in all other areas of work.

3. Horn Effect: The individual’s performance is completely appraised on the basis of a negative quality or feature perceived. This results in an overall lower rating than may be warranted. “He is not formally dressed up in the office. He may be casual at work too!”.

4. Excessive Stiffness or Lenience: Depending upon the raters own standards, values and physical and mental makeup at the time of appraisal, ratees may be rated very strictly or leniently.

   Some of the managers are likely to take the line of least resistance and rate people high, whereas others, by nature, believe in the tyranny of exact assessment, considering more particularly the drawbacks of the individual and thus making the assessment excessively severe. The leniency error can render a system ineffective. If everyone is to be rated high, the system has not done anything to differentiate among the employees.

5. Central Tendency: Appraisers rate all employees as average performers. That is, it is an attitude to rate people as neither high nor low and follow the middle path. For example, a professor, with a view to play it safe, might give a class grade near the equal to B, regardless of the differences in individual performances.

6. Personal Biases: The way a supervisor feels about each of the individuals working under him - whether he likes or dislikes them - as a tremendous effect on the rating of their performances. Personal Bias can stem from various sources as a result of information obtained from colleagues, considerations of faith and thinking, social and family background and so on.

7. Spillover Effect: The present performance is evaluated much on the basis of past performance. “The person who was a good performer in distant past is assured to be okay at present also”.

8. Recency Effect: Rating is influenced by the most recent behaviour ignoring the commonly demonstrated behaviours during the entire appraisal period.

Therefore while appraising performances, all the above biases should be avoidd.