Figure 1.

Flow chart of study selection. Pooled ORs were calculated using the Mantel-Haenszel (M-H)Estimator. Study-level data were pooled using a random-effects model when I2 was > 50% or a fixed-effects model when I2 was < 50%.

Liu et al. Critical Care 2012 16:R109   doi:10.1186/cc11398
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