Which statement correctly describes the relationship among efficacy, effectiveness, and compliance in treatment outcomes?

• A. Effectiveness is approximately equal to efficacy multiplied by compliance.
• B. Efficacy equals effectiveness divided by compliance.
• C. Compliance equals efficacy plus effectiveness.
• D. Effectiveness equals efficacy plus compliance.

Answer: (A)

The key idea is that real-world treatment results depend on how closely patients follow the prescribed regimen. Efficacy reflects the maximum effect seen under ideal conditions with perfect adherence, while compliance (adherence) measures how well patients actually follow the regimen in practice. Since the benefit you observe in the real world is limited by both how strong the treatment could be and how consistently people take it, the overall effectiveness is roughly the product of efficacy and compliance. In other words, effectiveness ≈ efficacy × compliance, so if adherence is perfect, effectiveness matches efficacy; if adherence is partial, the observed effect is reduced accordingly. This simple multiplicative relationship captures why both a strong treatment effect and good patient adherence are needed to achieve optimal outcomes.