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Table 1 Potential confounders considered in the analyses

From: Vigorous regular leisure-time physical activity is associated with a clinically important improvement in back pain – a secondary analysis of randomized controlled trials

Potential confounder

Description

Sex

Male, female

Age

Continuous

Body mass index

<18.5, 18.5-24.9, 25-30, >30 continuous

Daily smoking

Yes, no

Level of education

Elementary (1-9 y), secondary (10-12 y), university (13-16 y), higher academic education (>16 y)

Pain intensity at baseline

Mean score on the Chronic Pain Questionnaire based on current pain intensity, worst pain intensity during the last 4 weeks and average pain intensity during the last 4 weeks, continuous

Pain-related disability at baseline

Mean score on the Chronic Pain Questionnaire based on how pain hindered daily, recreational-, social-, and family activities as well as interfered with work during the last 4 weeks, continuous

Pain duration at baseline

<1 month, 1-3 months, 4-6 months, >6 months

Previous episodes of pain

Yes, no

Pain location 

Neck pain, back pain or equally bad pain in both locations