Asymmetry in which graphical display indicates publication bias?

• A. Line graphs
• B. Funnel plots
• C. Bar charts
• D. Scatter plots

Answer: (B)

In meta-analysis, publication bias shows up when smaller studies with null or non-significant results are less likely to be published. A funnel plot is used to spot this. On a funnel plot, each study’s effect size is plotted against a measure of precision (often the standard error). If there’s no bias and little heterogeneity, the points are spread symmetrically around the true effect, with more precise studies clustered near the top and less precise ones fanning out below, forming a roughly funnel-shaped pattern.

When publication bias exists, the plot becomes asymmetric because studies on one side (often the smaller, less precise ones with non-significant results) are missing. That missing portion distorts the symmetry and signals possible bias. It’s important to note that asymmetry can also arise from other factors like true differences between studies or selective reporting, so it suggests a potential issue rather than proving it.

Other graphs—line graphs, bar charts, and scatter plots—don’t specifically visualize publication bias in the same way and aren’t used to detect this bias pattern.