In a meta-analysis, heterogeneity between studies is measured by the I² statistic. An I² of 75% indicates:
- A 75% of the variation is due to chance alone and heterogeneity is low
- B High heterogeneity — 75% of total variance across studies is attributable to between-study variation rather than sampling error ✓
- C Moderate heterogeneity — the meta-analysis can proceed without concern
- D Publication bias accounts for 75% of effect size variance
Correct answer: B. High heterogeneity — 75% of total variance across studies is attributable to between-study variation rather than sampling error
Explanation
I² ranges from 0–100% and quantifies the proportion of total variation in effect estimates attributable to true between-study heterogeneity (rather than chance). I² 0–25% = low heterogeneity, 25–50% = moderate, 50–75% = substantial, >75% = considerable heterogeneity. At I² = 75%, a random-effects model is essential, and subgroup analyses or meta-regression should explore sources of heterogeneity.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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