In a meta-analysis, the I² statistic is reported as 78%. What does this MOST accurately indicate?
- A 78% of studies in the meta-analysis had positive results
- B 78% of the total variability in effect estimates is due to true heterogeneity rather than sampling error ✓
- C The pooled estimate has a 78% probability of being the true effect
- D There is a 78% chance that the summary estimate is biased
Correct answer: B. 78% of the total variability in effect estimates is due to true heterogeneity rather than sampling error
Explanation
I² quantifies the proportion of total variability in effect estimates across studies that is attributable to true heterogeneity (between-study variance) rather than random sampling error; an I² of 78% indicates considerable heterogeneity. Values of 25%, 50%, and 75% correspond to low, moderate, and high heterogeneity respectively. High I² warrants a random-effects model and cautious interpretation of the pooled estimate.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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