Psychological distress will be analyzed by a composite measure of occupational distress, perceived stress, and depression. For occupational distress, both occupational status and job strain will be analyzed. Not only occupation type but also period of service in the current and previous occupation will be noted to evaluate occupational status. Average daily working hours, commuting method (car, bus, subway, walk or other) and commuting time (less than 30 minutes, 30 minutes to 1 hour, 1 hour to 2 hours or more than 2 hours) will also be recorded. Job strain will be investigated by means of a job content questionnaire (JCQ) validated in the Korean language.