Table 2.

Association between sleep disturbance and WOMAC pain score over time using mixed-effects model in entire cohort

Sleep disturbancea	Model 1		Model 2
	β	95% CI	β	95% CI
1	Reference		Reference
2	0.73	0.32, 1.14	0.48	0.07, 0.89
3	1.54	1.07, 2.01	1.24	0.77, 1.71
4	3.98	3.21, 4.75	3.84	3.07, 4.62
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)

β beta coefficient, CI confidence interval