What research method involves the in-depth study of a single individual or group?

The case study method is characterized by its in-depth examination of a single individual or a small group. This approach allows researchers to gather detailed and rich qualitative data, which can lead to a deep understanding of complex issues, behaviors, or psychological phenomena. By focusing on the intricacies of a specific case, whether it's a person, a family, or a group of individuals with shared experiences, the case study can illuminate unique insights that broader studies may overlook.

The flexibility of case studies also permits the exploration of various aspects of the subject’s life, including personal history, social context, and psychological factors. This method is particularly useful in psychology, allowing clinicians to develop hypotheses and understand atypical or extreme cases in a way that is not possible with other methodologies.