2.2. Worker selection
Factories were asked to use the following inclusion and exclusion
criteria to select employees as participants. The inclusion
criteria were: (1) employment in the current factory for over 12
months; (2) frontline workers. The exclusion criteria were: (1)
employees in administration, design and logistics; (2) illiterate; (3)
seasonal migrant workers.
About 60 workers fulfilling the inclusion/exclusion criteria were
identified by the factory management in each factory (based on
sample size estimation for the subsequent intervention trial) and
invited to participate in the study. Totally 3638 frontline workers
were invited and 3479 workers agreed to participate in the survey
(95.6% response rate).