Table 2
Outcomes and statistical methods
| Outcomes | Definition | Statistical method |
|---|---|---|
| Number of recurrences of spinal pain (3–27 months follow up) in relation to individual follow-up time | i) A positive answer on the weekly SMS for spinal pain ii) Minimum of 1 week without report of spinal pain prior to the recurrence | A hierarchical negative binomial regression model with pain free weeks included as exposure time. Intervention effects were expressed as incidence rate ratios |
| Length of spinal pain episodes | The number of consecutive weeks the child was affected by spinal pain | A mixed effects linear regression model with subject as random effect, outcome log transformed. Intervention effects were expressed as β-coefficient |
| Total number of pain weeks in relation to individual follow-up time | Total number of weeks a child was affected by spinal pain in the entire follow-up period | A hierarchical negative binomial regression model with follow-up time included as exposure time. Intervention effects were expressed as incidence rate ratio |
| Global perceived effect after 2 weeks | Dichotomized into two groups: “Much better” (1) and “Slightly better, the same or worse” (2 to 7). | A logistic regression model. Intervention effects were expressed as odds ratios |
| Change in pain intensity after 2 weeks | Rated on an 11-point Numerical Rating Scale with ‘0’ being ‘worst pain’ and ‘10’ being ‘no pain’ | A linear regression model. Intervention effects were expressed as β-coefficient |