Sample and Setting
Because it has been determined that noise levels of 80 dBA and above pose a hazard to workers (NIOSH, 1998), factories that reported noise levels greater than 80 dBA for an 8-hour period and provided hearing protection for their workers were eligible for the study. Four manufacturing plants in Chiang Mai Province fulfilled these criteria and were selected for inclusion, including an electronics plant, a wood furniture factory, a food canning factory, and a paper mill. In addition, these companies