Case Study in AP Psychology

How to recognize a case study in a research scenario

A case study trades breadth for depth. A survey collects a little data from many people. A case study collects a lot of data from very few, using interviews, observation, medical records, and test scores, sometimes gathered over months or years.

Case studies don't belong to just one unit. They fall under Science Practice 2, Research Methods and Design, which runs through all five units of the course. Two skills there apply directly: determining which research design a study used, and evaluating the design elements of non-experimental methods. That's why a case study can show up in Unit 1 (Biological Bases of Behavior), Unit 2 (Cognition), Unit 3 (Development and Learning), or Unit 5 (Mental and Physical Health).

The tell is what the researcher did. If a scenario describes one patient, one family, or one unusual individual investigated intensively through many kinds of data, it's a case study. A small sample alone isn't enough, since some experimental designs also study a single person. If the researcher doesn't manipulate an independent variable, the study is non-experimental, and a case study is one possible design.

Phineas Gage and H.M.: what single cases taught the course

The strongest argument for case studies is that some situations can't be created in a lab. No ethics board would approve damaging a person's brain to see what happens. When an accident or surgery does it, a careful case study is the best evidence available.

Phineas Gage was a railroad worker who survived an iron rod passing through his frontal lobe in 1848. Reports of his personality change afterward pointed researchers toward the frontal lobe's role in personality and impulse control. His case connects to the brain content in Unit 1, Biological Bases of Behavior.

H.M. (Henry Molaison) had much of his hippocampus and surrounding medial temporal lobe removed to treat severe epilepsy. Afterward he couldn't form new explicit long-term memories, but he could still improve at motor tasks he didn't remember practicing. His case helped separate explicit from implicit memory and tied the hippocampus to forming new memories. That links him to Unit 1 for the brain structures and to the memory content in Unit 2, Cognition.

Where a single case's conclusions stop

Gage and H.M. show both the value and the limits. Their cases generated hypotheses that later research tested with larger samples. On their own, they couldn't confirm those hypotheses.

The limits to name on the exam:

• Low generalizability. One person, usually chosen because they're unusual, may not represent anyone else.
• No causal conclusions. Nothing is manipulated and nothing is controlled, so other explanations can't be ruled out. Gage's injury, his recovery, and his life circumstances all changed at once.
• Researcher bias. One investigator interpreting one person's story may notice what fits their expectations and overlook what doesn't.
• Unreliable reports. Much of the data comes from self-report or other people's recollections, which can be incomplete or distorted. Accounts of Gage's personality change came largely from people who knew him, not from standardized measures.

If an answer choice says a case study "proves" that X causes Y, it's wrong. A case study can suggest a cause. It can't establish one.

Judging a case study in Article Analysis and Evidence-Based questions

A researcher spends two years interviewing and testing one patient with a rare brain injury. A multiple-choice item built on that scenario might ask you to name the design or pick its main limitation. Common limitations to consider are limited generalizability and the inability to establish cause and effect. Choose the one the question actually asks about.

In the Article Analysis question, a summarized article could describe an in-depth, non-experimental case study. Identify the design from what the researchers did, rather than from the number of participants alone. A top answer names it as a case study, explains that its findings can't be generalized because it rests on one or a few unusual cases, and states that the study can't show causation. For the part that asks about ethics, case studies usually involve detailed personal information, so confidentiality is a natural guideline to identify if the summary describes it. Researchers often protect identity with initials, which is why Henry Molaison was known only as H.M. until his death. Informed consent can also apply, especially when the participant has a condition that affects their ability to agree. This ethics piece is also part of Science Practice 2.

In the Evidence-Based question, one of the three sources may be a case study. This draws on Science Practice 4, Argumentation. You can cite the case study as evidence, but a strong answer weighs it carefully and treats a single case as support for a claim rather than proof. Pairing it with a larger study from another source makes your reasoning more convincing.

Case study vs. longitudinal study vs. naturalistic observation

Case studies and longitudinal studies both can stretch over years, which is where the mix-up comes from. Ask whether the defining feature is repeated measurement over time (longitudinal) or in-depth investigation of one case or a small number of cases (case study). A study can be both. A researcher who intensively studies one patient's memory through interviews, records, and repeated testing over ten years is running a case study that's also longitudinal.

Naturalistic observation is the other near neighbor. It means watching behavior in its normal setting without interfering, usually across many individuals and using one data source, observation. A case study can include observation, but it pulls together many kinds of data about one case. Focus on the in-depth look at a single case and the mix of sources when you pick between them.