Table 3.

Linear random- and mixed-effects models of percentage mobility during sleep and sleep efficiency. Analysis of 83 sleep periods among 68 seamen on board 20 Royal Norwegian Navy vessels

Model components	Percentage mobility during sleep (%)						Sleep efficiency (%)
	Random-effects model		Mixed-effects model 1		Mixed-effects model 2a		Random-effects model		Mixed-effects model 1		Mixed-effects model 2a
	β	SE	β	SE	β	SE	β	SE	β	SE	β	SE
Fixed effects
Intercept	13.59*	0.82	13.13*	1.02	−0.93	5.57	86.63*	0.77	86.89*	1.14	98.93*	5.77
Gender (0=male, 1=female)			−2.80b	1.63					−1.08	1.98
Coffee drinker (0=no, 1=yes)			3.04*	1.15	3.89*	1.11			−0.91	1.41
Nicotine user (0=no, 1=yes)			−2.77*	1.13	−2.75*	1.09			1.60	1.39
Sleeping hours (0=night, 1=day)			1.70b	1.16	1.81b	1.12			−1.59	1.44
Equivalent noise level					0.21*	0.10					−0.19b	0.10
Noise events per hour
1.1 or more					3.05*	1.12					−3.45*	1.33
0.5-1.1					2.94*	1.12					−2.75*	1.34
<0.5					Reference						Reference
Random effectsc
Within-worker variance	15.10	2.63	16.66	2.46	13.32	2.42	21.41	3.79	21.83	4.00	21.95	3.98
Between-vessel variance	9.30	4.06	7.42		5.06	2.77	6.12	3.87	5.77	3.97	2.29	2.87
Percentage of variance explained by the fixed effects			1.3		24.9				−0.3		12.0

*P < 0.05, ^aThe variable “mean LAmax of noise events” was also entered in the mixed-effects model 2, but were not retained (P > 0.2) in the final model, ^bP ≤ 0.2: The variable was retained in the model, ^cBetween-worker variance could not be calculated. SE = Standard error