A systematic review reports I² = 78% across 12 included studies. Which statement about this finding is MOST accurate?
- A There is substantial heterogeneity and a random-effects model is more appropriate than fixed-effects ✓
- B 78% of variance in results is due to sampling error alone
- C The studies should be pooled using fixed-effects model since I² does not reach 100%
- D The review should be discarded as results are unreliable
Correct answer: A. There is substantial heterogeneity and a random-effects model is more appropriate than fixed-effects
Explanation
I² measures the proportion of total variability due to between-study heterogeneity rather than chance. Values of 25%, 50%, and 75% correspond to low, moderate, and substantial heterogeneity respectively. At I²=78%, there is substantial heterogeneity, and a random-effects model accounts for this between-study variance appropriately. Fixed-effects model assumes all studies estimate the same true effect, which is untenable here. High I² warrants subgroup analysis to identify sources of heterogeneity.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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