In a clinical trial, the Odds Ratio (OR) for an outcome comparing a new drug to placebo is 0.4 (95% CI 0.2–0.8). How should this be interpreted?

• A The new drug increases the odds by 40%
• B The new drug reduces the odds of the outcome by 60% compared to placebo ✓
• C The result is not statistically significant
• D The new drug reduces risk by 40% compared to placebo

Explanation

OR of 0.4 means the odds of the outcome in the drug group are 0.4 times that in the placebo group, representing a 60% reduction in odds (1 – 0.4 = 0.6 = 60%). The 95% CI (0.2–0.8) excludes 1.0, so the result is statistically significant. OR and RR are not the same; OR approximates RR only when outcome is rare.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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