Review

Association between lung function and exacerbation frequency in patients with COPD.

Int J Chron Obstruct Pulmon Dis. 2010 Jan 1; 5: 435-44.
Randomized Controlled Trial

Panax ginseng C.A Meyer root extract for moderate chronic obstructive pulmonary disease (COPD): study protocol for a randomised controlled trial.

Trials. 2011 Jan 1;12:164.
Multicenter Study

The distribution of COPD in UK general practice using the new GOLD classification.

Eur. Respir. J. 2014 Apr 1;43(4):993-1002.