In the first case-control epidemiological study of the effects of tobacco Müller recorded a statistically significant correlation between cigarette smoking and lung cancer.  See Alfredo Morabia, "Quality, originality, and significance of the 1939 'Tobacco consuption and lumg carcinoma' article by Mueller, including translation of a section of the paper," Prev. Med., 55 (2012), 171-177. Full text of the 2012 paper from PubMedCentral at this link.