A systematic review pools data from 5 studies on a new antihypertensive drug. The I² statistic is reported as 78%. What does this indicate?

• A High heterogeneity; a random-effects model is preferred ✓
• B 78% of the variance in results is due to sampling error
• C The meta-analysis included 78% of all published studies
• D Low heterogeneity; a fixed-effects model is preferred

Explanation

The I² statistic quantifies the proportion of total variability in study estimates due to heterogeneity (true differences between studies) rather than chance. An I² of 78% indicates high heterogeneity (values >75% are considered substantial), and a random-effects model is preferred as it accounts for between-study variance. Fixed-effects models assume all studies estimate the same underlying true effect.

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

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