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Liu, Yong, Janet B. Croft, Lynda A. Anderson, Anne G. Wheaton, Letitia R. Presley-Cantrell, và Earl S. Ford. The Association of Chronic Obstructive Pulmonary Disease, Disability, Engagement in Social Activities, and Mortality Among US Adults Aged 70 Years or Older, 1994–2006. Dove Medical Press, 2014.

Liu, Yong, et al. The Association of Chronic Obstructive Pulmonary Disease, Disability, Engagement in Social Activities, and Mortality Among US Adults Aged 70 Years or Older, 1994–2006. Dove Medical Press, 2014.