“If this is full-time, most commonly 1800 – 0600, and usually continuing after midnight. This category is used only for permanent night work” (Hurrell, 2003, no page).
Hurrell, K. (2003, March). Statistics on shiftwork: Survey questions, definitions and classifications. Retrieved August 3, 2005, from http://www.iwh.on.ca/media/images/Shiftwork.pdf