Fig. 2. Funnel plot of use of antifibrinolytic compared with placebo or no treatment on the proportion of patients requiring allogeneic erythrocyte transfusion according to a transfusion protocol. A funnel plot is a scatter plot of the treatment effect estimated from individual studies (logarithm of odds ratio [OR],  horizontal axis ) against a measure of study size (SE of logarithm of OR,  vertical axis ).  Solid line is pooled OR;  dashed line is null effect. Effect estimates from small studies should scatter more widely at the bottom of the graph, with the spread narrowing among larger studies. In the absence of bias, studies are symmetrically distributed around the pooled OR, and the plot resembles a symmetric inverted funnel. Asymmetric funnel plots may indicate publication bias or be due to exaggeration of treatment effects in small studies of low quality.  Solid circles are double-blind studies;  open circles are open-label studies and/or studies showing no significant beneficial effect.