Daniyar, P. R. A., A. Kristiyanto, and S. S. Rahardjo. “Meta-Analysis the Association Between Chronic Obstructive Pulmonary Disease Comorbidity and COVID-19 Mortality”. Journal of Epidemiology and Public Health, vol. 6, no. 2, Apr. 2021, pp. 222-31, https://jepublichealth.com/index.php/jepublichealth/article/view/395.