What is a funnel plot?
A funnel plot is a scatterplot of the effect size versus the standard error of the effect size for a set of studies. It is used to graphically assess publication bias and small-study effects by allowing for comparison of studies of different sizes. An asymmetrical plot suggests the presence of bias and can indicate the presence of other factors that may have an impact on the results. It can also help to identify areas of high heterogeneity and areas of potential subgroup differences.  