Figure 2. Changes of FEV1 (the upper panel) and FEV1 to FEV ratio (the lower panel) between COPD patients and control participants.

Abbreviations: 95% CI, 95% confidence interval; COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in one second; FVC, forced vital capacity; WMD, weighted mean difference. WMD is denoted by the center of a solid diamond, and the length of solid line cross this diamond denotes its 95% CI. The hollow diamond with a vertical broken line denotes overall risk estimate. The solid vertical line is set at the null value (WMD = 0.0).