A case study is a non-experimental research method that examines one individual or small group in extreme depth, often over time. It produces rich, detailed (usually qualitative) data but cannot establish cause-and-effect and is hard to generalize to larger populations.
A case study is the deep dive of psychological research. Instead of testing hundreds of participants, a researcher focuses on one person or one small group and gathers everything they can, including interviews, observations, medical records, and test results, often over a long stretch of time. The result is rich, detailed, mostly qualitative data you simply can't get from a survey or a lab experiment.
The trade-off is the heart of what AP Psych wants you to understand. Because there's no manipulated variable, no random assignment, and no control group, a case study can never prove what caused a behavior. And because the sample is one unusual person, you can't confidently generalize the findings to everyone else. So why use one? Sometimes a case study is the only ethical or practical option, like studying a patient with rare brain damage. You can't ethically remove someone's hippocampus to see what happens, but if an accident or surgery already did, a case study lets psychologists learn from it.
Case studies sit in Topics 1.2 and 1.4, where you have to compare research methods and explain why a psychologist would pick one over another. The core skill is matching the method to the question. Need cause and effect? That's an experiment (Topic 1.3). Need detailed information about one individual's behavior or mental state? That's a case study. Case studies also do quiet work across the rest of the course. Much of the Unit 1 brain content under 1.4.A (what the hippocampus, frontal lobes, and other structures do) was originally pieced together from famous case studies of brain-damaged patients. And in Topic 7.10, Freud built psychodynamic personality theory almost entirely on clinical case studies, which is exactly why critics call that theory unscientific and unfalsifiable.
Keep studying AP Psychology Unit 7
Cause-and-Effect Relationship / The Experimental Method (Unit 1)
This is the contrast the exam loves most. Experiments manipulate variables with random assignment, so they can establish causation. A case study just describes one case in depth, so the most it can ever show is what happened, not why. If a question asks which method determines cause and effect, the answer is never a case study.
Brain Structures and Functions (Unit 1)
A lot of what you learn under 1.4.A came from case studies of brain damage. Patients like Phineas Gage (frontal lobe injury changing personality) and H.M. (hippocampus removal destroying the ability to form new memories) are case studies. Researchers couldn't ethically create these injuries, so studying the people who already had them was the only way in.
Measuring Personality (Unit 7)
Freud and other psychodynamic theorists built their entire theory of personality on case studies of individual patients. That's also the standard critique you should know for Topic 7.10. A theory built on a handful of unusual cases is hard to generalize and hard to test scientifically.
Qualitative Research (Unit 1)
Case studies are the classic example of qualitative research. They produce words, narratives, and detailed descriptions rather than numerical data you can run statistics on. That richness is the strength, and the lack of measurable, generalizable numbers is the weakness.
Case studies show up most often in multiple-choice questions about choosing a research method. A typical stem describes a research goal and asks which design fits, and the case study is the right answer when the goal is gathering detailed information about a single individual's behavior or mental state, or studying something too rare or unethical to recreate. The classic trap answer works the other way. If the stem asks which method determines cause-and-effect relationships, the case study is wrong and the experiment is right. On the free-response side, the Article Analysis Question can hand you a study and ask you to identify its method and evaluate it. If the study follows one person or one small group in depth, name it as a case study and be ready to state its key limitation, that the findings can't be generalized and no causal claim can be made.
Both can follow people over time, which is where the confusion starts. The defining feature of a case study is depth on ONE case (one person or one small group), and it may or may not last a long time. The defining feature of a longitudinal study is the time dimension itself, tracking the SAME group of participants (often a large sample) across years to measure how they change. Ask yourself what the study is built around. One fascinating individual means case study. Tracking change over time in a group means longitudinal.
A case study is an in-depth, usually qualitative analysis of one individual or small group, often conducted over time.
Case studies cannot establish cause-and-effect relationships because nothing is manipulated and there is no control group; only experiments can show causation.
Findings from a case study are hard to generalize because the sample is a single, often unusual, case.
Psychologists choose case studies when a phenomenon is rare or when manipulating it would be unethical, such as studying patients with existing brain damage like Phineas Gage or H.M.
Freud's psychodynamic theory of personality (Topic 7.10) was built on case studies, which is exactly why it's criticized as hard to test and hard to generalize.
On the AP exam, pick the case study when the goal is detailed information about one person's behavior or mental state, and pick the experiment when the goal is causation.
A case study is a non-experimental research method where a psychologist studies one individual or small group in extreme depth using interviews, observations, and records, often over time. It appears in Topics 1.2 and 1.4 as one of the methods you compare against experiments and other designs.
No. A case study has no manipulated variable, no random assignment, and no control group, so it can only describe what happened, not prove why. Only a true experiment can establish a cause-and-effect relationship.
A case study is defined by depth on one case (one person or small group), while a longitudinal study is defined by tracking the same group of participants over a long period to measure change. A case study can be longitudinal, but the single-case focus is what makes it a case study.
Usually because the situation is rare or impossible to recreate ethically. Researchers learned what the hippocampus does for memory from H.M., a patient whose hippocampus was surgically removed, because no one could ethically cause that damage in an experiment.
Phineas Gage, whose frontal lobe injury changed his personality, and H.M., who lost the ability to form new long-term memories after hippocampus removal, are the two classics. Both connect directly to the Unit 1 brain structures you learn under 1.4.A.