Fig. 1From: Can roflumilast, a phosphodiesterase-4 inhibitor, improve clinical outcomes in patients with moderate-to-severe chronic obstructive pulmonary disease? A meta-analysisStudy flow diagram. ACP, American College of Physician; CENTRAL, Cochrane Central Register of Controlled Trials; COPD, chronic obstructive pulmonary disease; RCT, randomized controlled trialBack to article page