Table 1.

Potential confounders of the association between work-related risk factors and sick leave in patients with neck or upper extremity complaints

Potential confounders	Categorization
Individual factors
Age	Continuous (per year)
Sex	Male versus female
Smoking	Present versus previous smoker
Education	Primary versus secondary; college/university
Pain copinga: retreating (seven items)	Continuous (scale 7–28)
Pain copinga: worrying (nine items)	Continuous (scale 9–36)
Distress (six items)	Continuous (scale 1–9)
General health
ACSM position standc	Norm not met versus norm met
Norm healthy activity	Norm not met versus norm met
Perceived healthd	Continuous (scale 1–5)
Vitalityd (four items)	Continuous (scale 0–100)
Quality of life	Continuous (scale 1–5)
Characteristics of the complaint
Kind of complaint	Localized versus generalized
Duration of the complaint	Categorical (<1, 1–4 weeks; 1–6 , >6 months)
History of neck/upper limb complaints	History versus no history
Musculoskeletal co-morbidity	Yes versus no
Other co-morbidity	Yes versus no
Work-related psychosocial factors (%)
Decision authorityf (three items)	Tertiles (low, medium, high)
Job demandsf (five items)	Tertiles (low, medium, high)
Co-worker supportf (four items)	Tertiles (low, medium, high)
Job-securityf	Low security versus high security
Job as perceived cause of complaint	Yes versus no

^aPain Coping Inventory (Kraaimaat and Evers 2003; Kraaimaat et al. 1997)

^bFour Dimensional Symptom Questionnaire (Terluin 1998)

^cAmerican College of Sports Medicine Position Stand (American College of Sports Medicine Position Stand 1990)

^dMedical Outcomes Study 36-item Short Form Health Survey (Ware and Sherbourne 1992)

^ePhysical workload questionnaire (Bot et al. 2004)

^fJob Content Questionnaire (Karasek et al. 1998); %work-related psychosocial factors were considered as potential confounders in the relation between work-related physical factors and sick leave