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Forest plot of odds ratio for low birth weight. Pooled OR = 1.73, 95 % CI: 1.64, 1.82; Heterogeneity chi-squared = 148.65 (d.f. = 42), p = 0.000, I-squared (variation in ES attributable to heterogeneity) = 71.7 %; Test of ES = 1: z = 20.06, p = 0.000
