Sleep disturbances are associated with increased pain, disease activity, depression, and anxiety in ankylosing spondylitis: a case-control study

Table 5 Correlation coefficients between components of PSQI, demographic, clinical, and psychogenic variables (Spearman rho)

Variables	PSQI	Subjective sleep quality	Sleep latency	Sleep duration	Habitual sleep efficiency	Sleep disorders	Use of sleep medications	Daytime dysfunction
Age (years)	0.165**	0.073	0.142*	0.074	0.065	0.193**	0.135*	0.139*
Years of education	-0.149**	0.003	-0.206**	-0.083	-0.119*	-0.047	-0.186**	-0.099
ESR (mm/h)	0.163**	0.187**	0.086	0.070	0.171**	0.102	0.062	0.044
CRP (mg/dl)	0.164**	0.172**	0.072	0.034	0.159**	0.134*	0.040	0.125*
Disease duration (years)	0.094	0.051	0.091	0.011	-0.013	0.095	-0.014	0.133*
Morning stiffness (minutes)	0.250**	0.219**	0.185**	0.103	0.177**	0.173**	0.069	0.180**
Fingertip-to-floor distance (cm)	0.04	0.040	0.010	-0.038	-0.025	0.084	0.049	0.114*
Overall assessment of health (VAS)	0.386**	0.258**	0.241**	0.073	0.200**	0.359**	0.174**	0.375**
Nocturnal pain (VAS)	0.487**	0.324**	0.337**	0.181**	0.330**	0.364**	0.129*	0.388**
Total back pain (VAS)	0.485**	0.319**	0.297**	0.199**	0.295**	0.386**	0.176**	0.424**
BASMI	0.093	0.044	0.057	0.023	0.105	0.122*	0.025	0.065
BASDAI	0.479**	0.322**	0.327**	0.130**	0.214**	0.421**	0.206**	0.467**
BASFI	0.312**	0.198**	0.168**	0.052	0.119*	0.421**	0.128*	0.313**
SDS	0.467**	0.290**	0.346**	0.124*	0.178**	0.438**	0.167**	0.448**
SAS	0.522**	0.347**	0.384**	0.173**	0.236**	0.493**	0.169**	0.439**

* P < 0.05; ** P < 0.01. Spearman rho, <0.3, the weak correlation; Spearman rho, 0.3 to 0.5, the medium correlation; Spearman rho, >0.5, the high correlation. BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; BASMI, Bath Ankylosing Spondylitis Metrology Index; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; PSQI, Pittsburgh Sleep Quality Index; SAS, Self-rating Anxiety Scale; SDS, Self-rating Depression Scale; VAS, visual analogue scale.

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