Forest plot of only filter vs. only plain cigarette smoking and all lung cancer. Table 14 presents the results of a meta-analysis for all lung cancer based on 42 relative risk (RR) and 95% confidence interval (CI) estimates for only filter vs. only plain cigarette smoking. The individual study estimates are shown numerically and graphically on a logarithmic scale. The studies are sorted in order of sex within study reference (REF) within start year of study (START) within continent (CONT). In the graphical representation individual RRs are indicated by a solid square, with the area of the square proportional to the weight (inverse-variance of log RR). Arrows indicate where the CI extends outside the range allocated. Also shown are the combined random-effects estimates. These are represented by a diamond of standard height, with the width indicating the 95% CI.