Statistical analysis
Data analysis was conducted using STATA 15.0 (StataCorp, College Station, TX, USA) software. Six genetic models were analysed, as for Arg16Gly polymorphism, namely, the dominant model (GG+AG vs. AA), recessive model (GG vs. AG+AA), allele model (G vs. A), homozygous model (GG vs. AA), heterozygous model (AG vs. AA) and additive model (GG+AA vs. AG). We tested whether genotypic frequencies fall within the Hardy-Weinberg equilibrium (HWE) by the Chi-square test. The impact ofADRB2 polymorphisms (including Arg16Gly ,Gln27Glu) on the response to salbutamol in asthmatic patients was measured by odds ratio (OR) and 95% confidence interval (CI). The chi-square-based Cochran’s Q-test and Higgins (I2) statistics were used to assess heterogeneity among studies. The random effects model was adopted in case of evident heterogeneity (P H<0.10 or I2>50%). If no obvious heterogeneity existed, the fixed effects model was applied (P H≥0.10 and I2≤50%). To address significant heterogeneity, subgroup analysis and Galbraith plot analysis [24] were carried out. Subgroup analyses were performed by age (adult vs. children) and ethnicity (Caucasian vs. Asian). Sensitivity analysis was conducted by removing the study deviating from HWE. To evaluate the robustness of these results, sensitivity analysis was also employed by omitting one study at a time. Publication bias was assessed according to the asymmetry of the funnel plot. Begg’s and Egger’s tests [25] were also performed to evaluate publication bias and P <0.05 was interpreted as statistically significant.