Case study in psychology

Case study in psychology refers to the use of a descriptive research approach to obtain an in-depth analysis of a person, group, or phenomenon. A variety of techniques may be employed including personal interviews, direct-observation, psychometric tests, and archival records. In psychology case studies are most often used in clinical research to describe rare events and conditions, which contradict well established principles in the field of psychology. Case studies are generally a single-case design, but can also be a multiple-case design, where replication instead of sampling is the criterion for inclusion. Like other research methodologies within psychology, the case study must produce valid and reliable results in order to be useful for the development of future research. Distinct advantages and disadvantages are associated with the case study in psychology. The case study is sometimes mistaken for the case method, but the two are not the same.
Advantages.
One major advantage of the case study in psychology is the potential for the development of novel hypotheses for later testing. Second, the case study can provide detailed descriptions of specific and rare cases
Disadvantages.
Case studies cannot be used to determine causation. 
References.
^ Schultz & Schultz, Duane (2010). Psychology and work today. New York: Prentice Hall. pp. 201–202. .