Key Idea: Match the method to the question: experiments for cause, correlations for links, observation and self-report for real behaviour and inner experience.
Topic 2.4 at a glance
- Experiments — IV, DV, control, random allocation — the only method that shows cause.
- Non-experimental — Observation, case study, correlation — rich or realistic, but no cause.
- Self-report & sampling — Questionnaires/interviews; random/opportunity/self-selected/stratified samples.
Design · Method · Sample
IB-style questionExplain[6 marks]
A researcher wants to test whether background music improves focus. Explain which method they should use and why, and one limitation.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Which method shows cause? A true experiment (manipulate IV, control others, random allocation).
Correlation limitation? It can't show cause — third variable or reverse causation.
Why does sampling matter? A biased sample limits generalisability.
On Paper 2, always link the method to a strength and a limitation, and connect the sample to who the findings generalise to.