4.2.3 - Case studies

What case studies are

A case study is a research method that investigates one case in depth. The case is usually one individual, a very small group, or a rare situation. In psychology, case studies are used when the researcher wants a detailed picture of behaviour, experience and context rather than a broad numerical pattern from a large sample.

Case studies are useful when the case is unusual, complex or ethically impossible to create on purpose. A psychologist cannot deliberately cause brain damage, traumatic childhood separation or a rare clinical condition just to study the effect. If such a case already exists, a case study can help psychologists understand it carefully.

Case studies often produce qualitative data, such as interview answers, diary material, observations and descriptions of symptoms or experiences. They can also include quantitative data, such as test scores, questionnaire ratings, brain-scan results or performance on memory tasks. The key feature is not "only words"; the key feature is depth.

A detailed investigation can still be narrow in scope. Ten interviews about one individual remain evidence about that case; they do not become a representative sample of ten independent cases.

Building a case history

A good case study is not just a long anecdote. It is planned, recorded and checked so the account is as accurate as possible.

A psychologist might build a case history by combining:

Using several sources matters because each one has limits. A person's memory may be selective. A relative may interpret events through their own emotions. A test score may miss important context. Combining sources allows the researcher to compare evidence. The aim is not a vote in which the largest number of agreeing sources wins. A family interview and a medical note quoting the same family report are not two independent confirmations.

Some case studies are longitudinal, meaning the researcher follows the case over time. Others use retrospective data, meaning the researcher looks back at past records or memories to understand how the case developed.

AO2 scenario: Dr Kaur studies Eli, who developed sudden face-recognition problems after a cycling accident. She interviews Eli, observes him identifying objects and faces, checks hospital records, asks his family about everyday difficulties and gives standardised visual-processing tests every three months. This is a case study because Dr Kaur is building a detailed account of one rare case using several data sources.

Ethics need particular care. Case studies may include private medical, family or therapy information, so informed consent, confidentiality, anonymisation and the right to withdraw are important. If the case is famous or rare, anonymity can be difficult because small details may identify the person.

Why case studies matter

Case studies are linked to the idiographic approach in psychology. Instead of immediately trying to produce general laws about many people, the researcher studies the unique details of one case.

This does not mean case studies are only interesting stories. A single unusual case can challenge an existing theory, suggest a new hypothesis, or show that a psychological process is more complex than researchers previously thought.

A useful illustration is the case of H.M. Henry Molaison had surgery in 1953 to reduce severe epilepsy. Scoville and Milner (1957) reported that after bilateral medial temporal-lobe surgery, H.M. showed severe difficulty forming new long-term memories for everyday events, while some older memories and immediate memory abilities were relatively spared. The contrast suggested that retaining information briefly and forming enduring new memories could be affected differently. This challenged a simple view of memory as one undifferentiated ability and helped motivate further research. It did not, on its own, identify every memory system or isolate one brain structure from all neighbouring tissue. The original Scoville and Milner report (1957) described several surgical cases, including H.M.; his later intensive study is the case illustration here.

H.M. is useful for understanding why case studies matter:

A single case can also challenge an absolute claim. If a theory says that loss of one ability must always involve loss of another, a carefully established dissociation can count against that universal claim. That logical contribution differs from estimating how common a pattern is, which requires wider evidence.