A case study in psychology is a descriptive research approach used to obtain in-depth information about a person, group, or phenomenon. It is different from survey research, which involves asking a group of participants questions through interviews or questionnaires. Cast studies also tend to be far more in-depth than observational research in that they use multiple measures or records and focus on a single subject. (A multiple-case design can be used in some instances.) Case studies may be prospective or retrospective; prospective studies feature criteria that are established and include additional cases that meet those criteria as they become available, while retrospective studies use criteria to select cases from historical records. Case studies also tend to use qualitative data, such as interviews, but may occasionally use quantitative data as well, like questionnaires. They are often seen in clinical research, where the treatment of a specific individual is monitored to determine what is effective.

Case studies use techniques such as personal interviews, direct observation, psychometric tests, and archival records to gather information. They are used to explore causation in order to find underlying principles. However, they cannot be generalized to the overall population, as can experimental research, and they cannot provide predictive power, as can correlational research. Rather, they can provide extensive information for the development of new hypotheses for future testing, or about a rare or otherwise hard-to-study event or condition. As such, they are often seen in clinical research, where the treatment of a specific individual is monitored to determine what is effective.

For instance, a client in a mental health hospital could be studied as he progresses through a course of treatment involving individual counseling, group therapy and medication. While any results from the study could only be applied to that particular client, the results could inform a future hypothesis about the relative effectiveness of such treatment options.

Techniques Used in Case Studies

The most common techniques used to collect data for case studies are:

• personal interviews
• direct observation
• psychometric tests
• archival records

Advantages of Case Studies

One major advantage of the case study in psychology is the potential for the development of novel hypotheses for later testing. Case studies are used to explore ideas on a subject and can determine underlying principles. An "average" or "typical" case is often not the richest in terms of information, but with a case study, researchers can choose the most informative subjects to examine in depth. Picking and choosing data like this is impossible in experimental studies. This method can also provide incredibly detailed descriptions of specific and rare or otherwise hard-to-study cases. With rare events, such as specific injuries to the brain or sociopathic behavior, a case study allows for a detailed analysis of the behaviors and situations related to these events which could not be recorded ordinarily. Lastly, this type of research also allows for the observation of phenomenon in real-life situations.

Disadvantages of Case Studies

A researcher cannot draw cause and effect relationships from case studies. Even though a case study may indicate that a specific circumstance is associated with a particular trait or situation, it does not mean that all cases relate to those same factors. Case studies also cannot test hypotheses. While they can gather information to inform hypotheses, they cannot support or refute a prediction. Case studies cannot be generalized to the overall population, as in experimental research, nor can they provide predictive power, as in correlational research. The observations made in a case study are based on a very limited sample, and since this sample is not randomized or typically very large, the findings cannot be extrapolated to apply to broader contexts.

Well-Known Case Studies

Some famous case studies in psychology include:

• Phineas Gage: Gage was a rail construction foreman who survived an accident in which a tamping rod went through his skull and brain. The injury destroyed most of his frontal cortex, and subsequently had dramatic effects on his personality, therefore informing scientists about the connection between regions of the brain and personality and behavior.
• Freud and Little Hans: Sigmund Freud completed an extensive case study about a 5-year-old boy he called "Little Hans," exploring the reason for his phobia of horses.
• Little Albert: John Watson's study of classical conditioning in a 9-month-old boy named Albert examined whether it was possible to condition an otherwise emotionally stable child to fear a stimulus that most children would not find fearful.
• John Money and the John/Joan case: An examination of the impacts of sexual reassignment surgery on David Reimer.
• Genie: The case study of a child who was raised in total isolation and thought of as "feral."
• Jean Piaget's studies examined phases of cognitive and intellectual development.