Figure 6.

Funnel plots of effect sizes extracted in the systematic review

Funnel plots show how the effect sizes of RRs from individual studies systematically vary according to the SE of their observations. Because each child age interval has a different average effect size, as estimated by our models, we plotted the residuals against the SE of the observations. The residuals are defined as the normalised RR of the study minus the age-specific fit. Many studies outside of the funnel would indicate study-level heterogeneity and indicate more deviation from the average effect size than would be expected from chance alone. RR=relative risk.