Figure 18From: Systematic review with meta-analysis of the epidemiological evidence relating smoking to COPD, chronic bronchitis and emphysema Funnel plot for ever smoking and emphysema. Funnel plot of the 28 relative risk estimates for ever smoking and emphysema included in the main meta-analysis in Table 5 against their weight (inverse-variance of log RR). The dotted vertical line indicates the fixed-effect meta-analysis estimate.Back to article page