1.1.2—Causality
- Syllabus
- First assessment 2027
- Objective
- 1.1.2
- Level
- SL
Causality needs a design that rules out alternatives
A causal claim says that changing one factor produces a change in another. Correlation is evidence of association, but it can also arise from a third variable, reverse direction or coincidence.
A strong causal design controls plausible confounds, establishes temporal order and measures the construct accurately. Random assignment strengthens internal validity; replication and appropriate sampling help judge whether the result transfers.
If sleep and memory scores correlate, stress or workload may affect both. A controlled intervention that changes sleep while measuring the same memory outcome provides stronger causal evidence than a single survey.
Random assignment does not guarantee a representative sample, and a statistically significant association is not automatically a causal effect.