A case-control study comparing 200 cases of bladder cancer with 200 controls finds an odds ratio of 3.2 (95% CI: 1.8–5.7) for cigarette smoking. A systematic review of 12 similar studies reports a pooled OR of 2.9 (95% CI: 2.4–3.5) with I² = 18%. Which statement about the systematic review finding is MOST accurate?
- A The narrow confidence interval and low I² support a consistent, reliable association ✓
- B High heterogeneity limits the reliability of the pooled estimate
- C The I² value indicates publication bias is absent
- D A random-effects model must be used because studies are from different populations
Correct answer: A. The narrow confidence interval and low I² support a consistent, reliable association
Explanation
An I² of 18% indicates low between-study heterogeneity (threshold: <25% low, 25–75% moderate, >75% high). The narrow 95% CI (2.4–3.5) reflects high precision across pooled studies, supporting a consistent and reliable association. I² quantifies the proportion of variability due to heterogeneity rather than chance; it does not assess publication bias (Funnel plot/Egger's test do that). Low heterogeneity allows a fixed-effects model to be considered, although a random-effects model is not mandatory.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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