Interpreting an interaction effect
In a 2 × 2 study, a medication reduces anxiety in patients who also receive therapy but has no effect in patients who do not receive therapy. This result indicates:
Answer C: explanation for every choice
A
A main effect of medication alone would mean it helps regardless of therapy.
B
The medication clearly affects anxiety in the therapy group.
C
Correct. The medication's effect depends on the level of the other variable (therapy), which defines an interaction.
D
In a properly randomized factorial design, both variables are manipulated, so this is an effect, not a confound.
TakeawayInteraction: one variable's effect depends on the level of another.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID ps151.