2. Methods
2.1. Participants
The data used in this study was taken from the VI National Survey on Working Conditions (NSWCs) which was conducted in Spain by the Spanish National Institute of Safety and Hygiene in the Workplace (NISHW) in 2007. The objectives of that survey were to identify the frequency of exposure to various occupational hazards and characterize the most frequent occupational exposures, determine which of the factors of the labor environment influence the health of the workers, and evaluate the preventative activities undertaken by companies.
The survey process was carried out by a company called Sigma Dos between December 2006 and April 2007. The sampling procedure was undertaken in various stages, stratifying by conglomerate, randomly selecting the primary and secondary sampling units (municipalities and sections) and workers by random routes and established quotas.