In the behavioral observation scale (BOS) approach to performance appraisal, employees are also evaluated in terms of critical incidents. In that respect, the BOS is similar to the BARS. However, BOS appraisers rate subordinates on the frequency of the critical incidents as they are observed to occur over a given period. Ratings are assigned on a 5 point scale, and the evaluation yields a total score for each employee, obtained by adding the ratings for each critical incident. The behavioral incidents for the rating scale are developed in the same way as those for the BARS, through identification by supervisors or other subject matter experts. Similarly, the BOS meets equal employment opportunity guidelines because it is related to actual behaviors required for successful job performance.