“…Time taken to fall asleep was categorised as 20 min or less, 21-40 min and more than 40 min (Carskadon et al, 1986;Valent, Sincig, Gigli, & Dolso, 2016). Sleep disturbance was assessed using the General Sleep Disturbance Scale (Choi, Kim, Kim, & Kim, 2012;Lee, 1992), which shows high validity among shift workers and reduced recall bias (Carney et al, 2011). It consists of 21 items related to initiation insomnia, maintenance insomnia, sleep quality, sleep quantity, daytime functions and medication/self-help for sleep.…”