A lower mortality rate was associated with smoking cessation in all studies (Table 2). Odds ratios ranged from 0.29 to 0.84, and the combined odds ratio was 0.54 (95% confidence interval [CI], 0.46-0.62). Four studies had 95% CIs that included 1.00. The Zelen test for homogeneity was not significant (P=.61), suggesting that the differences in the results of the individual studies were compatible with chance. The estimate of between-study variance was negative. Consequently, the combined odds ratio and 95% CI using a random effects model were identical to those of a fixed effects model (odds ratio, 0.54; 95% CI, 0.46-0.62) (Figure 1).