Table 2.

Association of neck–shoulder pain (NSP) trajectory class with sick leave (days/month) and work ability (ordinal scale 0–10) over 1 year, referencing low NSP

GEE models (classes)	N	Sick leave				Work ability
		P value	RR	95% CI Lower	95% CI Upper	P value	OR	95% CI Lower	95% CI Upper
Model 1
Low NSP	292		1.00				1.00
Moderate NSP	208	<0.001	3.28	1.89	5.68	<0.001	2.45	1.87	3.21
Strong NSP	178	<0.001	8.98	4.78	16.89	<0.001	8.64	6.38	11.69
Severe NSP	70	<0.001	17.64	9.36	33.23	<0.001	15.07	9.94	22.85
Model 2
Low NSP	286		1.00				1.00
Moderate NSP	204	<0.001	3.25	1.87	5.64	<0.001	2.40	1.83	3.16
Strong NSP	174	<0.001	8.61	4.54	16.33	<0.001	9.03	6.62	12.31
Severe NSP	68	<0.001	16.00	8.17	31.34	<0.001	14.77	9.63	22.66
Model 3
Low NSP	277		1.00				1.00
Moderate NSP	199	<0.001	3.11	1.75	5.52	<0.001	2.43	1.84	3.20
Strong NSP	165	<0.001	7.58	3.91	14.71	<0.001	8.12	5.91	11.16
Severe NSP	66	<0.001	13.83	6.72	28.49	<0.001	12.93	8.50	19.67

RR estimates, indicating the relative increase in the number of days on sick leave per month, were obtained using GEE with a Poisson distribution for days on sick-leave (measured at 4-week intervals). ORs indicating the likelihood of a 1-unit reduction in work ability, were obtained using GEE with a multinomial distribution for work ability (measured at 12-week intervals).

Model 1: unadjusted.

Model 2: adjusted for age, gender and body mass index.

Model 3: additionally, adjusted for occupational sector (four categories, referencing administration) and physical work load.

GEE, generalised estimation equation; RR, relative risk.