Table 1 Candidate predictor overview

 Age

Unique identifier (CPR number)^a

Years

 Sex

Unique identifier (CPR number)^a

Male or female

 Professional educational level

Baseline questionnaire

None, short-cycle higher education < 2½ years, medium-cycle higher education 3½-4 years, long-cycle higher education > 4 years, other

 Employment status

Baseline questionnaire

Employed, subsidised employment, leave of absence, unemployed, student/ apprentice/ vocational training, early retiree/ retiree/ voluntary early retiree, other

 QuickDASH

Baseline questionnaire

As in “outcome variable”

 Duration of symptoms

Baseline questionnaire

Months

 Pain intensity

Baseline questionnaire; Numeric pain rating scale (NPRS) [37,38,39]

Typical shoulder pain the last 14 days ranging from 0 “no pain” to 10 “worst pain imaginable

 Sick leave

Baseline questionnaire

Whole days with any sick leave due to current episode of shoulder pain

 Movement impairment classification

Pathoanatomic diagnosis was assessed by the physiotherapist at first consultation and based on that, the patients were classified in movement impairment groups after data collection [36]

3 groups based on movement impairment: Hypomobility (capsulitis, arthritis, post fracture etc.), Hypermobility (instability, trauma etc.), and Aberrant motion (rotator cuff, impingement, pain with movement etc.)

 Fear avoidance

Baseline questionnaire; two questions from the Danish short form version of Örebro Musculoskeletal pain questionnaire [40,41,42,43,44]

Two questions ranging from 0 to 10 (0 = no fear avoidance, 10 = high fear avoidance) with a sum score from 0 to 20

 Self-rated ability to cope with the pain

Baseline questionnaire; one questions from the Danish version of Örebro Musculoskeletal pain questionnaire [40,41,42,43,44]

One question ranging from 0 to 10 (0 = no ability, 10 = complete ability)

 Self-rated risk of the pain becoming persistent

Baseline questionnaire; one question from the Danish version of Örebro Musculoskeletal pain questionnaire [40,41,42,43,44]

One question ranging from 0 to 10 (0 = no risk, 10 = very large risk)

 Pain catastrophizing

Baseline questionnaire; two questions from the pain catastrophizing scale [45,46,47,48]

Two questions ranging from 0 to 10 with a sum score from 0 to 20 (0 = no pain catastrophizing, 20 = high pain catastrophizing)

 Mental wellbeing

Baseline questionnaire; WHO Mental wellbeing Index (WHO-5) [49]

A five-item questionnaire with a sum score ranging from 0 (low mental wellbeing) to 100 (high mental wellbeing)

 Health-related quality of life

EQ 5D-5L index [50, 51]

The index contains five dimensions each assessed by one question regarding; mobility, self-care, usual activities, pain/discomfort and anxiety/depression [52]. Utility values derived from a general population sample is used to calculate an index score ranging from − 0.6 to 1, where 1 represents a perfect health-related quality of life [52,53,54].