Table 2 Candidate prognostic factors for participants included in the study*

Age

Calculated from CPR and date of first visit

Years

Continuous

Sex

Calculated from CPR

Female/Male

Categorical

Normal weight [34]

1. Weight

2. Height

1. kg

2. cm

Categorical

Calculated from weight and height. ‘Not normal weight’: BMI < 18.5 or > 24.9 < kg/m2;‘Normal weight’: BMI 18.5–24.9 kg/m2

LBP intensity [23]

LBP now.

Worst LBP intensity in the last 14 days.

Typical LBP intensity in the last 14 days.

Numerical Rating Scale (NRS) (0–10)

0: No pain;

10: Worst possible pain

Continuous (0–10)

Averaged on present LBP, worst LBP last 14 days and typical LPB last 14 days

Episode duration

Approximately when was the onset of your low back pain or leg pain (sciatica)?

Days since onset of LBP

Continuous

Months calculated from days since onset of LBP

Previous LBP episodes

Have you had previous episodes of low back pain or leg pain (sciatica)?

Yes/No

Dichotomous

Leg pain

Leg pain intensity now.

Worst leg pain (sciatica) intensity in the last 14 days.

Typical leg pain (sciatica) intensity in the last 14 days.

Numerical Rating Scale (NRS) (0–10)

0: No pain;

10: Worst possible pain

Dichotomous

Presence of leg pain: > 0 on ≥ 1 item

Pain in other parts

Over the last 2 weeks, have you been bothered by pain in body parts other than you have marked on the previous drawing?

Yes/No

Dichotomous

Disability [35, 36]

23-item Roland Morris Disability Questionnaire (RMDQ)

Yes/No for each item

Converted to a proportional score (0-100)

0: No disability;

100: Extremely severe disability

Depression [37,38,39]

During the past month have you often been bothered by feeling down, depressed, or hopeless?

During the past month have you often been bothered by little interest or pleasure of doing things?

Ordinal (0–10)

Dichotomized:

Not Depressed < 6;

Depressed ≥ 6

Anxiety [37]

Do you feel anxious?

Ordinal (0–10)

Dichotomized:

Not anxious < 5;

Anxious ≥ 5

Fear-avoidance [37]

Physical activity might harm my back.

I should not do physical activities which (might) make my pain worse.

Ordinal data (0–10)

Dichotomized:

No fear-avoidance < 7;

Fear-avoidance ≥ 7

Risk of persistent pain [40]

In your view, how large is the risk that your current pain may become persistent?

Ordinal data (0–10)

Dichotomized: High risk ≥ 7; Low risk < 7.

Categorical

Social isolation [37]

Do you feel socially isolated?

Ordinal data (0–10)

Dichotomized:

Not socially isolated < 2;

Socially isolated ≥ 2

Present work participation

What is your present work participation?

1: Regular employment (fulltime or part time); 2: Flex job; 3: Studying; 4: Undertaking rehabilitation; 5: Unemployed; 6: Receiving disability pension; 7: Receiving retirement pension; 8: Housewife or househusband; 9: Other

Dichotomized:

‘No regular employment or studying’ 2, 4–9;

’Regular employment or studying’ 1 or 3

Sick leave

Have you taken sick leave for low back pain or leg pain (sciatica) in the last 3 months?

Yes/No

Dichotomous