Case Study in AP Psychology

In AP Psychology, a case study is a non-experimental research design that examines one individual or small group in great depth, often over time. It gives rich detail and generates hypotheses, but it can't show cause and effect or be generalized to a larger population.

What is Case Study?

A case study is a deep dive into a single person, family, or small group. Instead of collecting a little data from many people, the researcher collects a lot of data from very few. That data can come from interviews, observation, records, and tests, sometimes gathered over months or years.

Think of it as the opposite of a big survey. A survey trades depth for breadth. A case study trades breadth for depth. Because there's no manipulation of an independent variable and no random assignment, a case study is a non-experimental design (Science Practice 2.C). That means it can describe what happened and suggest why, but it can't prove what caused what. And because the sample is tiny and usually unusual, its findings may not apply to people in general.

Why Case Study matters in AP® Psychology

Case studies live in Science Practice 2 (Research Methods and Design), a course-wide skill that shows up in every unit rather than in one numbered topic. They connect most directly to 2.A (identify the type of research design used in a study) and 2.C (evaluate the appropriate use of design elements in non-experimental methods). Ethics questions under 2.D also apply, since case studies collect detailed, personal information about real people, so confidentiality matters a lot. Because research methods run through the whole course, you can meet a case study scenario in a question about brain damage, memory, development, or psychological disorders.

How Case Study connects across the course

Longitudinal Study (Science Practice 2)

Many case studies follow one person over time, so they can look longitudinal. The difference is sample size. A longitudinal study tracks a group of participants over time, while a case study zooms in on one person or a very small group. A case study can be longitudinal in timing without being a longitudinal study in design.

Qualitative Research (Science Practice 2)

Case studies usually produce qualitative data, meaning words, descriptions, and interview responses instead of numbers. That's why they're great at capturing a full human story but weak at producing statistics you can generalize.

Correlational Studies and Experiments (Science Practice 2)

Like a correlational study, a case study can't establish causation. Only an experiment with a manipulated independent variable, a control group, and random assignment can do that. A useful way to picture it is that a case study gives a researcher an idea, and an experiment tests whether that idea holds up.

Confidentiality (Science Practice 2)

When you study one person in detail, it gets easy to identify them. That makes protecting participant identity especially important in case studies, which ties this design directly to the ethics skill in 2.D.

Is Case Study on the AP® Psychology exam?

No released FRQ has used the term "case study" verbatim, but research design scenarios are a core part of the AP Psych exam. Here's what you need to be able to do.

• Identify it (2.A). A question describes a researcher studying one patient, one family, or one unusual individual in depth. You name the design as a case study.
• Evaluate it (2.C). You explain the strength, which is rich, detailed information about rare or unusual cases that would be impossible or unethical to create in a lab. Then you explain the limits. Results can't be generalized to a population, and no cause-and-effect conclusion is possible.
• Spot the trap. If an answer choice or argument says a case study "proves" something causes something else, it's wrong. Watch for researcher bias too, since one investigator interpreting one person's story can see what they expect to see.
• Check the ethics (2.D). Ask whether the participant's identity was kept confidential and whether informed consent was obtained.

Case Study vs Longitudinal Study

Both can stretch over long periods, which is where the confusion comes from. The key question is how many people are being studied. A case study examines one individual or a very small group in depth. A longitudinal study follows a group of participants over time to see how a variable changes. If a scenario says "a researcher followed one patient for ten years," call it a case study. If it says "researchers followed 500 children from age 3 to age 18," call it a longitudinal study.

Key things to remember about Case Study

• A case study is an in-depth investigation of one person or a small group, often using interviews, observation, and records.

• Case studies are non-experimental, so they can never establish cause and effect.

• Because the sample is tiny and often unusual, case study findings usually can't be generalized to a larger population.

• The main strength of a case study is rich detail about rare situations that researchers couldn't ethically or practically create in an experiment.

• Case studies are often used to generate hypotheses that later get tested with experiments or larger studies.

• Confidentiality is a major ethical concern in case studies because detailed information about one person can make them easy to identify.

Frequently asked questions about Case Study

What is a case study in AP Psychology?

A case study is a non-experimental research design that examines one individual or small group in great depth, often over time. It falls under Science Practice 2, where you identify research designs (2.A) and evaluate non-experimental methods (2.C).

Can a case study prove cause and effect?

No. A case study has no manipulated independent variable, no control group, and no random assignment, so it can only describe and suggest possible explanations. Only a true experiment can establish causation.

How is a case study different from a longitudinal study?

A case study focuses on one person or a very small group, while a longitudinal study follows a larger group of participants over time. A case study can last years and still be a case study, because what defines it is the depth of focus on so few people.

Are case study results generalizable?

Usually not. The sample is tiny and often chosen because the person is unusual, such as someone with a rare brain injury. That means the findings may not represent the general population.

Why do psychologists use case studies if they have so many limits?

Case studies let researchers study rare or extreme situations that can't be ethically recreated in a lab, like the effects of a specific brain injury. They also generate hypotheses that later research can test with larger samples and experimental designs.