A forest plot is a graph that displays the results of multiple studies in a meta-analysis. It shows the estimated effect size from each study, the overall pooled estimate, along with confidence intervals. This graph helps readers assess the consistency and strength of evidence across studies.
These plots depict effect sizes on the horizontal axis and include a vertical reference line for no effect. For each experiment, it displays a point estimate for the effect and a confidence interval (CI).
The forest plot below displays 13 studies and their estimates of the effectiveness of a Bacillus Calmette-Gúerin (BCG) vaccine in preventing tuberculosis (TB), visually highlighting which studies favored the vaccine and the overall combined effect.
Overall, the green diamond indicates the studies favor the treatment group that received the vaccine over the control group which did not receive it. However, there are differences between the studies. Studies have CIs of different widths. Some CIs include the null value of zero (no effect), while others do not. One study’s point estimate even favors the control group! Several other estimates fall right on the no effect line.
