There is power in a good story. You may have used case study stories for many reasons, including when advocating for a project. Personal testimonial from participants who have had a positive experience can be very persuasive. However, this is not what is meant by ‘case study’ in evaluation. For an evaluator, the quality of a case study hinges on the methods used to collect and analyse the data and the writing or presentation of the story. The evaluator will select case studies that are relevant to the outcomes or issues the evaluation seeks to explore. You can have a case study of a single individual, groups of individuals, an object, even a place or a situation. A range of different kinds of data may be pieced together in a case study to tell a story relevant to the questions that inform the evaluation.
It is important to remember that a case study story is particular to an individual case; because one participant experienced something during a project, this does not necessarily mean that all participants did, or that any future participants will. This is why it is vital to select your cases carefully, so that they can genuinely help to illuminate the particular issues you are investigating.