Fig. 2

Rates of postoperative complications in subgroups defined according to risk of bias (see text for details) with odds ratios (ORs) and 95% confidence intervals (CI). The pooled OR and 95% CI are shown as the total. The size of the box at the point estimate of the OR gives a visual representation of the “weighting” of the study. The diamonds represent the point estimate of the pooled ORs and the length of the diamonds is proportional to the CI