Table 1

Potential prognostic factors and corresponding bibliographical references to definition and psychometric properties of the factors

Potential prognostic factor	Measurement	Categorisation in the analyses
Age	Age at baseline.	Continuous.
Neck disability24	Normalised Neck Disability Index (NDI%).	Continuous, 1–100 0 = ‘no disability’ and 100 = ‘complete disability’
Average pain intensity40	Average pain intensity during the previous week measured on an 11-point Numeric Rating Scale (NRS).	Continuous, 0–10 0 = ‘no pain’ and 10 = ‘pain as bad as it could be’
Depression41	Self-rating version of the Montgomery Åsberg Depression Rating Scale (MADRS-S).	Continuous, 0–54 0 = ‘no depressive symptoms’ and 54 = ‘severe depression’
Fear of movement42 43	The Tampa scale of kinesiophobia.	Continuous, 17–68 A sum score of 17–68, where higher score indicate higher fear of movement.
Catastrophising44	The six-item catastrophising subscale from the Coping Strategies Questionnaire (CSQ).	Continuous, 0–36 Each item of the subscale had a score of 0–6, where a high score indicated a high degree of catastrophising.
Social support45	Item numbers 5 and 14 of the Swedish Multidimensional Pain Inventory (MPI-S).	Continuous, 1–12 Each item with a score of 0–6, where 0 = ‘no social support’ and 12 = ‘high social support’.
Recovery expectation31	The answer to the question; ‘Do you think that any intervention or exercise will lead to recovery?’	Continuous, 1–5 5-point ordinal Likert scale from 1 = ‘No, definitely not’ to 5 = ‘Yes, completely recovered’.
Chronic widespread pain46	Derived from a pain drawing.	Yes; pain in all four quadrants of the body together with spinal pain.
Leisure physical activity47	‘How much have you, in general, moved or exerted yourself physically during leisure time in the past year’.	No/low intensity; very little/an occasional walk or similar/every day physical activity like gardening, cleaning/low intensity physical activity eg, walking or similar at least once a week. Moderate/high intensity; more strenuous physical activity, eg, jogging, swimming, etc, at least once a week/regular high intensity physical activity, eg, running, ball sports, etc.
Physical workload48	‘How physically strenuous has your work or daily activity been the past 12 months?’	Mostly sedentary. Low/heavy work load; low physical work load but mobile/quite physically strenuous work/physically strenuous work.
Dual-working	A combination of three items: Working/not working. What does your household look like? Who is primarily responsible for and performing the housework in your family?	Yes; (1) working, (2) living together with children and/or another adult person and (3) having the responsibility for the housework. No; any other combination of the three items (see the Methods section).