Table 4

Multivariable model: competition level—Pee Wee and Bantam players only (adapted from Knol and Vander Weele)25

Level of competitionStrata 1Strata 2Risk ratio (95% CI) of strata 1 versus strata 2p
value
Met the PA volume recommendations (ie, ≥42 hours/6 weeks)Did not meet PA volume recommendations (ie, <42 hours/6 weeks)
CasesControlsIRR
(95% CI)
p
value
CasesControlsIRR
(95% CI)
p
value
Imputed participation exposure+imputed PA volume
 Non-elite173961.00
(reference)
NA20193 2.45
(1.33 to 4.51)
0.004 2.45
(1.33 to 4.51)
0.004
 Elite172610.89
(0.46 to 1.74)
0.7357512.00
(0.85 to 4.78)
0.1772.24
(0.99 to 5.13)
0.054
Sensitivity analysis 4.1: imputed participation exposure+raw PA volume
 Non-elite142621.00
(reference)
NA17140 2.36
(1.24 to 4.46)
0.009 2.36
(1.30 to 4.46)
0.009
 Elite101980.61
(0.29 to 1.26)
0.1814341.49
(0.49 to 4.51)
0.4802.47
(0.88 to 6.99)
0.089
Sensitivity analysis 4.2: raw imputed participation exposure+imputed PA volume
 Non-elite173961.00
(reference)
NA20193 2.46
(1.33 to 4.53)
0.004 2.46
(1.33 to 4.53)
0.004
 Elite172610.87
(0.45 to 1.69)
0.6837511.97
(0.83 to 4.68)
0.1242.26
(0.99 to 5.14)
0.052
Sensitivity analysis 4.3: raw participation exposure+raw PA volume
 Non-elite142621.00
(reference)
NA17140 2.37
(1.24 to 4.49)
0.009 2.37
(1.24 to 4.49)
0.009
 Elite101980.59
(0.28 to 1.23)
0.1574341.42
(0.47 to 4.31)
0.5532.41
(0.85 to 6.84)
0.097
  • Bolded, significant finding (ie, 95% CI do not cross 1.00).

  • Final  model: log odds (number of concussions)=β01(PA)+β2(competition level)+β3(PA×competition level), adjusted for clustering by team and offset by participation hours.

  • IRR, incidence rate ratio; NA, not applicable; PA, physical activity.