Google also tries to point out predictable traps in performance reviews, which are often done with input from a group. The company has compiled a list of “cognitive biases” for employees to keep handy during these discussions. For example, somebody may have just had a bad experience with the person being reviewed, and that one experience inevitably trumps recollections of all the good work that person has done in recent months. There’s also the “halo/horns” effect, in which a single personality trait skews someone’s perception of a colleague’s performance.