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All-cause smoker versus never-smoker mortality rate ratio (RR) among urban and rural Chinese men in two prospective studies, by time period (about 1995 or about 2010) and by age started smoking regularly
Each study followed about 200 000 men. Each group-specific CI (including that for never-smokers, given by the width of the shaded strip) reflects the variance of the log risk in that one group, so comparisons of RRs use variances from more than one group.
