Assessment of Publication Bias
The presence of publication bias was evaluated using the Begg’s funnel plot (4), which is a measure of the proportion (in the X-axis) against the standard error of the proportion (in the Y-axis). Each open circle represents an individual study in the meta-analysis. The line in the centre indicates the pooled proportion and the other two lines indicate the 95% CI. The proportion estimates from smaller studies are expected to be scattered above and below the summary estimate, producing a triangular or funnel shape, if there is no publication bias.