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Clinical research methods: RCTs and neuroimaging
Edexcel IAL Psychology · WPS04 Clinical Psychology and Psychological Skills
Spec 8.3.1 adds two methods to those from Units 1 and 2: randomised controlled trials (RCTs) in clinical psychology, and neuroimaging (structural and functional scanning) in clinical psychology.
Randomised controlled trials
An RCT tests whether a treatment works.
- Participants are randomly allocated to the treatment group or a control group (placebo, waiting list or another treatment).
- Random allocation spreads participant variables evenly, so differences in outcome can be put down to the treatment.
- Often double-blind: neither participants nor researchers know who gets which treatment, reducing demand characteristics and experimenter bias.
Examples in Topic H: DeRubeis et al. (2005) compared cognitive therapy, paroxetine and placebo; Walsh et al. (2006) compared fluoxetine with placebo; Attia et al. (2019) compared olanzapine with placebo.
Evaluating RCTs
- Strengths: high internal validity; cause and effect; the 'gold standard' for treatment evidence; replicable.
- Weaknesses: ethical issues in withholding treatment from controls; strict inclusion criteria and ideal conditions may reduce generalisability to routine practice (which is why Hans and Hiller used effectiveness studies); therapies are hard to blind; expensive.
- The component guide asks where else RCTs would or would not suit, for example drug studies in biological psychology suit them; long-term development questions do not.
Neuroimaging in clinical psychology
| Scan | Type | What it shows | Clinical example |
|---|---|---|---|
| CAT (CT) | Structural | X-ray images of brain structure | Johnstone et al. (1976): enlarged ventricles in schizophrenia |
| MRI | Structural | Detailed images of structure using magnetic fields | Grey matter differences in schizophrenia |
| PET | Functional | Activity using a radioactive tracer (such as glucose) | Dopamine release and receptor studies |
| fMRI | Functional | Activity from changes in blood oxygen, no radiation | Brain responses to emotional pictures in depression or anorexia |
Evaluating neuroimaging
- Objective, scientific data; can compare patients and controls.
- Correlational: a difference in the brain may be a cause or an effect of the disorder, or of medication.
- Scanner settings are artificial; tasks may lack ecological validity.
- Safety: CT and PET involve radiation; MRI needs screening for metal (the June 2025 examiners credited safety screening, lying in the scanner and showing stimuli, and noted fMRI does not use a glucose tracer).
Worked example
Describe how an fMRI study could investigate whether people with depression respond differently to sad faces.
- Screen participants for metal and gain informed consent; recruit a depression group and a matched control group.
- Each participant lies still in the scanner and views sad and neutral faces in a counterbalanced order.
- fMRI measures blood oxygen changes, showing activity in areas such as the amygdala.
- Compare activity for sad versus neutral faces between groups.
Answer: Screening, scanner, stimuli, measure and comparison: specific to fMRI.
Check yourself
- Why are participants randomly allocated in an RCT?
- To make the study cheaper
- So participants can choose their treatment
- To increase the sample size
- To spread participant variables evenly so differences can be put down to the treatment
Show answer
To spread participant variables evenly so differences can be put down to the treatment. Randomisation controls participant variables.
- What does double-blind mean?
- Participants are blindfolded
- Neither participants nor researchers know who receives which treatment
- Two researchers analyse the data
- The study is repeated twice
Show answer
Neither participants nor researchers know who receives which treatment. It reduces demand characteristics and experimenter bias.
- What does fMRI measure?
- A radioactive glucose tracer
- X-ray images of bone
- Electrical activity on the scalp only
- Changes in blood oxygen linked to brain activity
Show answer
Changes in blood oxygen linked to brain activity. fMRI uses the BOLD signal; PET uses tracers.
- Which scan shows brain structure rather than activity?
- CAT
- PET
- fMRI
- A blood test
Show answer
CAT. CAT (CT) gives structural X-ray images.
- Which is an ethical issue specific to placebo-controlled RCTs?
- Participants are always deceived about the aim
- Animals are used
- The control group does not receive an active treatment
- Scans use radiation
Show answer
The control group does not receive an active treatment. Withholding treatment can harm controls.
- Explain why brain scans of patients cannot show that a brain difference causes a disorder.
Show answer
Scans only show a correlation between the disorder and the brain difference; the difference could result from the disorder or its medication rather than cause it.. Correlation without direction.
Sources
- Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification (issue January 2026)
- Pearson IAL Psychology component guide: WPS04 (Issue 2, November 2024)
- DeRubeis et al. (2005), Cognitive therapy vs medications in the treatment of moderate to severe depression, Archives of General Psychiatry 62
- Walsh et al. (2006), Fluoxetine after weight restoration in anorexia nervosa: a randomized controlled trial, JAMA 295
- Attia et al. (2019), Olanzapine versus placebo in adult outpatients with anorexia nervosa, American Journal of Psychiatry
- Johnstone, Crow, Frith, Husband and Kreel (1976), Cerebral ventricular size and cognitive impairment in chronic schizophrenia, The Lancet
- Pearson WPS04/01 examiners' report, June 2025
Last updated 8 November 2026. Spotted a mistake? Tell us.