Mark believes he received a less favorable performance review than his coworker Kathy due to bias from their mutual supervisor Paul. As the HR director, you cannot directly observe their work but must determine if bias occurred. The graphic rating scale format used may have influenced their scores due to issues like subjective interpretations and a lack of behavioral anchors. Other rating formats like behavioral observation scales could provide more reliable assessments but also have downsides like increased workload. Rating errors should be minimized by ensuring ratings are objective, valid, and free of biases.