A systematic review pools data from 8 RCTs using meta-analysis. The I² statistic is reported as 74%. What does this indicate?
- A 74% of the studies had methodological flaws
- B 74% of the studies favored the intervention
- C 74% of the variability in effect estimates is due to heterogeneity rather than chance ✓
- D The combined sample size is sufficient to detect a 74% difference
Correct answer: C. 74% of the variability in effect estimates is due to heterogeneity rather than chance
Explanation
I² (I-squared) quantifies the percentage of total variability in effect estimates across studies attributable to true between-study heterogeneity rather than random sampling error. I² of 74% indicates substantial heterogeneity (values >50-75% are considered high); this raises concern about combining the studies in a fixed-effects meta-analysis. A random-effects model or investigation of heterogeneity sources (subgroup analysis) is warranted. I² does not reflect study quality or the direction of effect.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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