Table 1 Characteristics of control and intervention groups of first and second grade of compulsory secondary education (CSE1–CSE2)

From: Backpack weight and back pain reduction: effect of an intervention in adolescents

  CSE1 CSE2
  Control Intervention p-value Control Intervention p-value
  n % n %   N % N %
Sex
 Boys 220 50.5 647 52.5 0.469 218 49.4 578 50.1 0.830
 Girls 216 49.5 585 47.5 223 50.6 575 49.9
Age
 12-years old 287 65.8 764 62.0 0.166  
 13-years old 149 34.2 468 38.0 278 63.0 698 60.5 0.359
 14-years old   163 37.0 455 39.5
Body mass index categories
 Underweight 22 5.1 28 2.3 0.018 10 2.3 25 2.2 0.928
 Average weight 255 58.5 691 56.1 266 60.3 678 58.8
 Overweight 114 26.2 369 30.0 121 27.4 324 28.1
 Obesity 45 10.3 144 11.7 44 10.0 126 10.9
School bag
 Two shoulder straps 403 92.4 1179 95.7 0.008 405 91.8 1107 96.0 <0.001
 Other type 33 7.6 53 4.3 36 7.9 46 4.0
Back lesion
 No 349 92.8 827 91.1 0.377 339 92.1 764 91.3 0.629
 Yes 27 7.2 81 8.9 29 7.9 73 8.7
Walking to school
 No 285 75.8 692 76.2 0.886 270 73.4 614 73.4 0.996
 Yes 91 24.2 216 23.8   98 26.6 223 26.6