IB Psychology HLTopic 5 — Research MethodsPaper 3 & IACore skill~10 min read
Case Studies: Depth Over Breadth
Almost every method in psychology asks how people in general behave. A case study asks something different: what can one person, studied properly, teach us that a thousand people never could? Sometimes the answer is nothing. Sometimes it rewrites a whole area of the subject.
📚 What you need to know
A case study is a detailed, in-depth investigation of one person or a small group.
It is used when someone has had a unique or rare experience that could not be created deliberately.
It collects qualitative data (interviews, observations, open questions) and often quantitative data too (memory tests, IQ tests, brain scans).
Using more than one method or more than one researcher is called triangulation, and it strengthens the findings.
Most case studies are longitudinal, following the same person over months or years.
The great strength is rich, holistic detail. The great weakness is that findings cannot be generalised.
Closeness between researcher and participant risks a loss of objectivity and therefore of validity.
Why anyone would study just one person
Because some things only happen once. You cannot ethically remove part of somebody’s brain to see what memory does without it. You cannot raise a child in isolation to test language development. When a rare case appears anyway, studying it in enormous detail is the only route to that knowledge.
The clearest example is the patient known as HM. Surgery for severe epilepsy removed part of his hippocampus, and afterwards he could no longer form new long-term memories. Researchers studied him for decades using interviews, observations, memory tasks, IQ tests and eventually brain scanning. From one man came the conclusion that the hippocampus is essential to forming new memories — and that memory is not a single system, because his skills kept improving even when he could not recall having practised.
The tall thin bar is the point. One participant, but measured from every angle and often over many years.
Triangulation: why one method is never enough
Because a case study rests on a single person, the researcher has to work hard to make the findings trustworthy. The main tool is triangulation: gathering more than one type of data, or involving more than one researcher, and checking whether they point the same way. If an interview, an observation and a memory test all tell the same story, that story is much harder to dismiss as one researcher’s interpretation.
You can triangulate data (different types), methods, or researchers. Naming which kind you mean is worth a mark on its own.
Strengths and limitations, properly explained
Point
Why it happens
What it means for the findings
Rich, in-depth data
Multiple methods over a long period
High explanatory power; you can say how something works, not just that it does
Holistic view
The whole person is studied, not one isolated variable
High ecological validity, because behaviour is seen in real context
Studies the unstudiable
Rare conditions cannot be created ethically
Access to knowledge no experiment could ever produce
Cannot generalise
One person, often unusual by definition
Findings describe that case; wider claims need other evidence
Loss of objectivity
Years of contact build a close relationship
Researcher bias creeps into what is recorded and reported, lowering validity
Hard to replicate
The case is unique and the methods are flexible
Low reliability, so credibility has to be built another way
The generalisation criticism is real, but do not overstate it. HM could not be generalised as a person, yet the finding that damage to a specific structure destroys a specific ability told us something about everybody’s brain. That is theoretical generalisability, and it is a strong point to make.
Ethics matter more here than almost anywhere. A case study describes one identifiable person in enormous detail, often over years. Anonymity, ongoing consent and the right to withdraw are not paperwork — they are the reason the person agreed at all.
🧩 What makes a case study credible
Use more than one method. Interviews plus observations plus objective tests, so the sources can be cross-checked.
Describe the methods fully. Anyone reading should be able to see exactly how the data were gathered.
Bring in a second researcher to code or interpret independently, so it is not one person’s reading.
Keep a reflexive journal. Record your own assumptions as you go, and report them honestly.
Follow the case over time. A single snapshot cannot show change, and change is usually the interesting part.
Be honest about limits. Stating clearly what cannot be generalised makes the rest more believable, not less.
Worked examples
WORKED EXAMPLE
Justify the choice of a case study
A woman survives a severe stroke and afterwards can understand speech perfectly but cannot produce it. Researchers plan a case study rather than an experiment. Explain two reasons why a case study is the appropriate method here.
Step 1: First reason — the condition is rare and cannot be created
You could never manipulate an IV to cause a stroke, so an experiment is both impossible and unethical.
Step 2: Second reason — depth is what the question needs
Using interviews, observations and language tasks gives rich, triangulated data about exactly which abilities survived and which did not.
Step 3: Add the wider value
The pattern of what is lost and what is kept supports theoretical generalisability about how language is organised in the brain.
Step 4: Acknowledge the cost
The findings describe this individual, so they cannot be generalised to a population without further evidence.
Rare unmanipulable condition + depth through triangulationtwo reasons means two developed points, not two labels
WORKED EXAMPLE
Evaluate one limitation
A researcher spends four years working closely with a family and publishes a case study about them. A reviewer questions the objectivity of the report. Explain this limitation and suggest how it could be reduced.
Step 1: Name the limitationLoss of objectivity through a close, long-term relationship with the participants.
Step 2: Explain the mechanism
The researcher may start to identify with the family, notice evidence that fits their expectations and quietly play down what does not.
Step 3: Name the damage
This is researcher bias, and it lowers the validity and credibility of the report.
Step 4: Give two realistic fixes
Researcher triangulation, so a second person codes the data independently; and reflexivity, keeping and publishing a record of the researcher’s own assumptions.
Loss of objectivity lowers validity; fix with triangulation and reflexivity“suggest how it could be reduced” always wants a named technique
💡 Exam tip
Name a real case. HM is the safest example and works for memory, biological approach and research methods questions alike.
Use the word triangulation and say which type you mean: data, method or researcher.
When you write “cannot be generalised”, add the exception: theoretical generalisability is still possible.
Longitudinal is a useful word here. It explains both the depth and the risk to objectivity in one term.
Ethics questions about case studies almost always want anonymity, informed consent and the right to withdraw.
Do not describe a case study as unscientific. It is systematic and evidence-based; it just answers a different kind of question.
⚠ Common mix-up
Thinking case studies are only qualitative. HM was given memory tests, IQ tests and MRI scans. Quantitative data is common.
Assuming a case study means one person. It can be a small group, a family, a school or an organisation.
Confusing triangulation with replication. Triangulation uses different sources on the same case. Replication repeats the whole study.
Saying case studies have low ecological validity. They usually have high ecological validity; it is generalisability they lack.
Treating “cannot generalise” as the only limitation. Loss of objectivity and low reliability are just as creditable, and less predictable.
Calling a case study an experiment because tests were used. No IV is manipulated, so it is not an experiment.
Up next: Reliability: Getting the Same Result Twice — the first of the research design ideas that decide whether any of these methods can be trusted.
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