1. [1] Global strategy for diagnosis, management, and prevention of COPD. Global initiative for chronic obstructive lung disease (GOLD). [Cited 2014 January]. http://www.goldcopd.org.
2. [2] COPD predicted to be third leading cause of death in 2030. Geneva: Global alliance against chronic respiratory disease, WHO statistics 2008. [Cited 2008 May 20]. http://www.who.int/gard/news_events/World_Health_ Statistics_2008/en/
3. [3] Jindal SK, Aggarwal AN, Chaudhry K, et al. A multicentric study on epidemiology of chronic obstructive pulmonary disease and its relationship with tobacco smoking and environmental tobacco smoke exposure. Indian J Chest Dis Allied Sci 2006;48(1):23-9.
4. [4] Jindal SK, Aggarwal AN, Gupta D. A review of population studies from India to estimate national burden of chronic obstructive pulmonary disease and its association with smoking. Indian J Chest Dis Allied Sci 2001;43(3):139-47.
5. Chronic obstructive pulmonary disease in non-smokers;SS;Lancet,2009