A systematic review pools four case-control studies. When Mantel-Haenszel pooled OR is calculated assuming a common effect, the I² statistic is 72%. The most appropriate next step is:

• A Proceed with fixed-effects model as I² <75%
• B Exclude outlier studies until I² falls below 50%
• C Report only qualitative synthesis without pooling
• D Apply a random-effects model and explore sources of heterogeneity ✓

Explanation

An I² of ≥50–75% indicates substantial to considerable heterogeneity; random-effects models (e.g., DerSimonian-Laird) account for between-study variance and are preferred over fixed-effects models. Exploring clinical and methodological sources of heterogeneity via subgroup analysis or meta-regression is the recommended next step. Excluding studies purely to reduce I² introduces selection bias. Abandoning quantitative synthesis is not required if heterogeneity can be explained.

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

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