Funnel plot

An example funnel plot showing no publication bias. Each dot represents a study (e.g. measuring the effect of a certain drug); the y-axis represents study precision (e.g. the inverse standard error or number of experimental subjects) and the x-axis shows the study's result (e.g. the drug's measured average effect).

A funnel plot is a graph designed to check for the existence of publication bias; funnel plots are commonly used in systematic reviews and meta-analyses. In the absence of publication bias, it assumes that studies with high precision will be plotted near the average, and studies with low precision will be spread evenly on both sides of the average, creating a roughly funnel-shaped distribution. Deviation from this shape can indicate publication bias.