However, case studies, like any other method GAO uses, have to meet two other criteria of  accuracy and lack of bias, in the sense that the evaluator's personal, preconceived opinions about a situation do not distort reporting and that the evaluator is scrupulously evenhanded in examining all sides of a situation.
There are two criteria relating to bias and accuracy that case studies have to meet.
Case studies do not have to meet any criteria for lack of bias.