Table 3

Prespecified study-level factors

FactorVariable typeCategoriesData available (%)
Year*Continuous(midpoint date of study sample frame)100
Clinical setting*CategoricalPrimary care; emergency care100
Study designCategoricalProspective; retrospective100
Data sourceCategoricalClinical encounter; insurer data; patient survey100
Imaging count methodCategoricalImaging event; imaging request100
Geographic regionCategoricalNorth America; Europe; Oceania; UK100
Imaging observation window*CategoricalImaging within 4 w; imaging within study period100
Imaging at first consultationCategoricalFirst; subsequent; any consultation96
Workers’ compensation CategoricalYes; no64
Duration of episode Categorical<3 months; ≥3 months40
Older age (>64 years) CategoricalYes; no38
Radicular syndrome CategoricalYes; no36
  • *Included in the adjusted model.

  • Study-level factors present in <85% of studies were ineligible for meta-regression modelling.