Study selection
The studies we included have to satisfy the inclusion criteria, as follows: (1) observational studies; (2) studies evaluated the relationship among ADRB2 polymorphisms (Arg16Gly, Gln27Glu) and salbutamol responsiveness in asthmatic patients; (3) studies offered valid data for calculating odds ratio (OR) and 95% confidence interval (CI); (4) studies reported short-term differences in the percentage change in FEV1 after salbutamol inhalation; and (5) human subjects. The following studies were excluded: (1) studies contained duplicate or unqualified data; (2) review, commentary, abstract, editorial, case report, letter and conference report; and (3) studies did not report the details for the assessment of good responders.