In one line: A case study zooms right in on one person or group to understand them in rich detail.
A case study trades breadth for depth. Rather than testing many people briefly, it studies one case thoroughly, often over time.
Case studies usually combine methods — interviews, observation, tests — to build a full picture. This links to the concept of measurement: many kinds of data are gathered to capture the case as completely as possible.
Memory hook: Depth over breadth. A case study goes deep on one case, not shallow on many.
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Key idea: Case studies suit rare, complex or unrepeatable situations that couldn't be studied any other way.
Features of a case study
Rare cases
Ideal for unusual conditions or events — e.g. a unique brain injury — that are too rare for an experiment.
Rich data
Combines several methods (interview, observation, tests) for deep, detailed, often qualitative data.
Real context
Studies the case in its real-life context, often over a long period (longitudinal).
Rare · Rich · Real
Take a patient with an unusual memory loss after brain damage. A case study uses interviews, memory tests and observation over months to map exactly what they can and can't remember — data no lab experiment on the general public could give. Many measurements build one rich picture.
Go further — higher-level insight: A single case can be hugely influential — but can't be generalised. One striking case (like a specific brain-injury patient) can reshape a whole theory, yet because it is a single, unusual case, we can't assume it applies to everyone. This depth-vs-generalisability tension is the key evaluation point.
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Key idea: Case studies give unmatched depth but are hard to generalise and can be subjective.
So case studies give deep, realistic insight into rare or complex cases, but a good evaluation notes their findings are hard to generalise, they can't show cause and effect, and they are open to researcher bias — especially when relying on a person's memory of the past.
Watch out: One case is not proof about everyone. A finding from a single case is a valuable clue, not a general law — resist over-generalising from one person.