Table 3.

Association between sleep disturbance and number of painful sites over time using mixed-effects model in entire cohort

Sleep disturbancea	Model 1		Model 2
	RR	95% CI	RR	95% CI
1	Reference		Reference
2	1.20	1.12, 1.28	1.14	1.07, 1.22
3	1.34	1.24, 1.44	1.25	1.16, 1.35
4	1.42	1.27, 1.58	1.31	1.17, 1.46
P for trend	< 0.001		< 0.001

Bold denotes statistically significant result

^a4-point sleep disturbance scale: (1) I am able to sleep without difficulty most of the time; (2) My sleep is interrupted some of the time, but I am usually able to go back to sleep without difficulty; (3) My sleep is interrupted most nights, but I am usually able to go back to sleep without difficulty; (4) I sleep in short bursts only. I am awake most of the night

Model 1: Univariable analysis

Model 2: Adjusted for fixed factors (age, sex, body mass index, physical activity, comorbidities, pain medications, ever smoking, emotional problems, employment, and education level)

RR relative risk, CI confidence interval