Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Efficacy refers to the ability of a treatment or intervention to produce desired results under ideal and controlled conditions, such as in a clinical trial or research setting.
Effectiveness refers to how well a treatment works in real-world settings and everyday practice rather than just controlled research environments.
Placebo effect: The placebo effect is the phenomenon where people experience improvements in their symptoms simply because they believe they are receiving an active treatment, even if it is actually inert.
Control group: A control group is a group of participants in an experiment who do not receive the experimental treatment but are used as a comparison against the group that does receive the treatment.