Of the 298 landfill waste landfill workers, all of them completed the questionnaire for demographic
information; 2 (0.7%) of them did not finish the questionnaire for work history; 49
(16.4%) of them were not administrated audiometric testing; 2 (0.7%) of them suffered from
significant hearing loss due to ototoxic drug use. No workers claimed any genetic risk for hearing loss. The 2 workers without work history did not finish audiometric testing neither; therefore, the 298 potential study subjects were reduced to 247 with a participant rate of 82.9%. Proportion of male workers for the 298 workers and the selected 247 workers were 81.0% and 80.6%, respectively; while the median age for the two populations were 39.0 and 38.0 years, respectively. Distributions and differences among subjects of selected characteristics were shown in