Table 5.

Association between Categories of Low Back Pain and Sleep Problems (Multivariable-Adjusted).

Category of low back pain	n	Cases of sleep problems, n (%)	Adjusted ORa (95% CI)	p-Value
1 (lowest)	998	112 (11.2)	1.00 (ref)	NA
2	739	133 (18.0)	1.15 (0.85-1.55)	0.366
3	477	134 (28.1)	1.34 (0.97-1.85)	0.077
4 (highest)	236	93 (39.4)	1.56 (1.06-2.30)	0.023

Notes: Job category was treated as a categorical variable, with administrative staff as the reference group. When low back pain was treated as an ordinal variable, p for trend = 0.014. Differences were considered statistically significant at p < 0.05.

^aAdjusted for job category, poor gastrointestinal condition, bowel problems, interpersonal stress at work, fatigue, depressive mood, and job and life satisfaction.

CI: confidence interval; NA: not applicable; OR: odds ratio; ref: reference.