Stata se version 15.0 for windows

The primary outcome was overall survival (OS), and the secondary endpoint was progression‐free survival (PFS). The effect sizes namely HR and 95% CI or P‐value of the dichotomous variable (“smokers” or “never‐smokers” of pretreatment smoking status) were extracted from each study and pooled to assess the prognostic value of pretreatment smoking status for SCLC. Cochran's Q test and Higgins' I² statistic were performed to evaluate the heterogeneity of the included studies based on I² and P‐values. If I² was ≤50% and P‐value was >0.10, the heterogeneity in different included studies was acceptable and we chose a fixed‐effects model to combine all studies, otherwise a random‐effects model was used. We also conducted sensitivity analysis to assess the influence of each study on the overall analysis and final result. Publication bias was assessed by Begg's funnel plot and Egger's linear regression. When the combined HR was >1, the range of 95% CI did not cross 1, and for two‐tailed P‐values <0.05, the result was considered statistically significant and served as an adverse prognostic factor. All statistical analyses were performed using the Review Manager software (RevMan V.5.3, Cochrane Collaboration, London, UK) and Stata/SE version 15.0 for Windows (Stata Corporation, College Station, TX, USA).