How to read a forest plot
Each horizontal line in a forest plot represents one study. The marker shows that study's point estimate of effect, and the line shows its confidence interval; a larger marker usually means the study carried more weight. A vertical line marks the no-effect value, often 1 for ratios or 0 for differences. Estimates whose intervals cross that line are individually inconclusive.
At the bottom, a diamond summarizes the pooled estimate across all studies, with its width showing the combined confidence interval. The pooled result borrows strength from every study at once, which is the point of combining them.
Heterogeneity and why pooling can mislead
Studies often disagree more than chance alone would predict, which is heterogeneity, commonly summarized with statistics such as I squared. High heterogeneity means the studies may be measuring meaningfully different things, so a single pooled diamond can paper over real differences in populations or methods.
This is general educational information, not medical advice. A meta-analysis summarizes existing evidence and does not by itself dictate care for any individual; clinical decisions belong with a qualified professional.