Since these possible causes, that is, current smoking, postnasal drip, COPD, asthma, and chest radiographic abnormality, are also observed in the population without chronic cough, the odds ratios (ORs) were analyzed to evaluate the impact of these factors on chronic cough. In multivariable analysis, only current smoking status, UACS, COPD, asthma, and abnormal chest radiographs were independently associated with chronic cough, and the adjusted ORs were 3.16, 2.50, 2.41, 8.89, and 2.74, respectively (Table 4). Current smoking, UACS, COPD, asthma, and abnormal chest radiographs were sequentially observed in subjects with chronic cough; however, the impact of chronic cough was strongest for asthma, followed in descending order by current smoking status, chest radiographic abnormality, UACS, and COPD.