Table 2 Overview of data collection

Gender

Male; Female

Categorical

Age

Date of birth

Continuous: years old at start treatment episode

Health insurance

Public health insurance (Puhi), private health insurance (Prhi)

Categorical: Puhi; Prhi; Unknown

Education

Highest level of education: Primary school, secondary education, higher education, university

Categorical: Low (primary); Middle (secondary, higher); High (university); Unknown

Urbanization rate

1 very high, 2 high, 3 moderate, 4 low, 5 very low

Categorical: High (3+2+1); Low (5+4); Missing values (1.3%) recoded as high urbanization rate

Complaints

Specialization of referring physician

GP or Medical specialist

Categorical: GP; Medical specialist

Reason for referral

As given by letter by the referrer; coded with ICPC (26) by researchers

Selection of patients with ICPC-code L03.00

Duration of complaint at start episode

< 2 days; 2–7 days; 1 week – 1 month; 1–3 months; 3–6 months; 6 months – 1 year; 1–2 years; > 2 years; unknown

Categorical: < 1 month; > 1 month; Missing values (1.0%) recoded as < 1 month

Recurrent complaint (appearing after a complaint-free episode of at least four weeks and at most two years)

Yes; No; Unknown

Categorical: Yes; No; Missing values (3.7%) recoded as no

Previous physical therapy for the same or other complaints in the last two years

Yes; No; Unknown

Categorical: Yes; No; Missing values (6.1%) recoded as no

Treatment

Treatment goals

Based on the International Classification of Functioning, Disability and Health (27); One main goal (out of 24) at the level of physical functions; One main goal at the level of activities (out of 11)

5 dichotomous variables; Missing values (0.6%) recoded as changing body position

Interventions

Based on Dutch classification; three interventions at most (out of 25) applied in at least 50% of the sessions

5 dichotomous variables; Missing values (16.1%) integrated in reference category

Therapists

Gender

Male; Female

Categorical: Male; Female; Missing values (2.1%) recoded as male

Age

Date of birth

Categorical: <45 years at January 1st, 2003; > 45 years at January 1st, 2003; Missing values (5.1%) recodes as > 45 years

Hours working per week

Patient-related number of hours

Categorical: <20 hours; 20–40 hours; >40 hours; Missing values (4.1%) recoded as 20–40 hours

Registration in quality register for manual therapy

Yes; No

Categorical: Yes; No

Additional training in LBP

Yes; No

Categorical: Yes; No; Missing values (4.1%) recoded as yes

Additional training in LBP guideline

Yes; No

Categorical: Yes; No; Missing values (4.1%) recoded as no

Feasibility of LBP guideline

1 item on questionnaire 10-point scale (1 = very bad; 10 = excellent; 7 = satisfactory)

Categorical: <7 points; >7 points; Unknown

Time since graduation

Date of graduation

Categorical: < 20 years since graduation; > 20 years since graduation; Missing values (6.2% recodes as > 20 years.

Practices

Group size

Number of therapists

Categorical: Single handed; Group practice