Table 1

Number of fractures, fracture incidences, and incidence rate ratios (IRR) per school year during the 8-year study period

School year1st2nd3rd4th5th6th7th8th
Intervention group
 Individuals (n)126711701004878758666568508
 Person-years (years)12641160999869751662566506
 Fractures (n)3726232218231111
 Fractures/1000 person-years (mean (95% CI))29.3 (20.6 to 40.3)22.4 (14.6 to 32.8)23.0 (14.6 to 34.5)25.3 (15.9 to 38.3)24.0 (14.2 to 37.9)34.7 (22.0 to 52.1)19.4 (9.7 to 34.8)21.7 (10.8 to 38.8)
Control group
 Individuals (n)21952009185216761543144712961188
 Person-years (years)21932000184916711541144212931187
 Fractures (n)3932383942434854
 Fractures/1000 person-years (mean (95% CI))17.8 (12.6 to 24.3)16.0 (10.9 to 22.6)20.6 (14.5 to 28.2)23.3 (16.6 to 31.9)27.3 (19.6 to 36.8)29.8 (21.6 to 40.2)37.1 (27.4 to 49.2)45.5 (34.2 to 59.4)
Incidence rate ratio (95% CI)1.65 (1.05 to 2.58)1.40 (0.84 to 2.35)1.12 (0.67 to 1.88)1.08 (0.64 to 1.83)0.88 (0.51 to 1.53)1.16 (0.70 to 1.93)0.52 (0.27 to 1.01)0.48 (0.25 to 0.91)
  • Data are presented as numbers, person-years, mean fracture rates, and risk ratios with 95% confidence intervals. Statistically significant group differences are bolded.