Similarity error is a negative tendency of the evaluator at the time of interview, assessment and performance appraisal. Here in, the evaluator's rating is biased towards the employees whom he or she perceives to be similar to himself or herself personally or professionally.
The similarity of personality, strengths, weaknesses and experiences leads to a bias in the rating by the evaluator. This is a huge area for concern because this inability of the evaluator often goes undetected and leads to an imbalanced verdict. This gap in understanding should not ideally influence an employee's rating. In organisations wherein the evaluator's subjective discretion plays a significant role, similarity error becomes the necessary evil. Therefore in order to escape this - organisations must adopt an objective measurement tool that quantitatively assesses the performance of a candidate. This way, the values of the organisation play a greater role, that those of the evaluator.
Psychometric tests, online assessment tests, 360 and 720 degree reviews, predictive analysis tests etc. hence play a crucial role here. They allow the organisation to understand the abilities quantitatively and therefore make an informed decision.
For example, an evaluator who went to the same school as that of the subject may tend to him a better rating. This is the reason why lobbies of certain educational institutes exist in organisations. Students of other colleges certainly face a disadvantage here. In this case it is also important to note that the organisation too suffers, as it creates a cohort of similar employees that affects the overall diversity of the work force and employer branding.
If an evaluator perceives himself as aggressive, and considers that to be a positive trait - then subjects who are polite yet assertive may be at a disadvantage.