“…A total of 1595 studies were screened; only thirty observational studies met the final inclusion criteria in the analysis ( Figure 1 ; Table A1 ) [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Main study characteristics of COPD and asthma analysis cohorts are abridged in Table 1 .…”