Study guides & original practice
Correlation vs causation in psychology
Interpret associations without assuming that one measured variable caused another.
By ExamCat · Original study lesson · Published September 24, 2026
Understand the method
Correlation measures an association. Reverse causation and third variables can explain an observed pattern. Random assignment in a well-controlled experiment helps separate a treatment effect from preexisting differences, while random sampling concerns how well the sample represents a population.
Worked example, step by step
A school survey finds that students reporting more sleep also report better concentration. No sleep schedule was assigned.
- Identify the measured variables: reported sleep and reported concentration.
- State the finding narrowly: the two reports are associated in this sample.
- Consider alternatives: stress could reduce both sleep and concentration; measurement errors could also matter.
- A causal test would need an ethical design that addresses confounding, rather than simply renaming the association an effect.
A mistake to watch for
A large correlation is not proof of causation. A correlation near zero also does not rule out a nonlinear relationship. Study design and the pattern in the data matter.
Try it yourself: three questions
Write an answer before opening the explanation. For calculations, keep your units and intermediate steps; for concepts, state the reason for your choice.
1. Ice cream sales and swimming accidents rise together. What third variable might matter?
Show answer and explanation
Hot weather can increase both. This is a possible confound, not proof of the actual explanation for a particular dataset.
2. What does random assignment help with?
Show answer and explanation
It helps balance preexisting differences between experimental groups in expectation, supporting a causal comparison when the rest of the design is sound.
3. Does random assignment guarantee a representative sample?
Show answer and explanation
No. Assignment determines groups within a study; sampling determines who enters it.
Build your next practice session
Mark the first step where your reasoning differed from the explanation. Turn that step into a question, answer it without looking, then change one condition in the example and explain what would change. A correct guess is a reason to revisit the method.
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