Table 3

Multivariable model: age group (adapted from Knol and Vander Weele)25

Age Group	Strata 1				Strata 2				RR (95% CI) of strata 1 versus strata 2	p value
	Met the PA volume recommendations (ie, ≥42 hours/6 weeks)				Did not meet the PA volume recommendations (ie, <42 hours/6 weeks)
	Cases	Controls	IRR (95% CI)	pvalue	Cases	Controls	IRR (95% CI)	p value
Imputed participation exposure+imputed PA volume
Pee Wee	12	376	1.00 (reference)	NA	11	127	2.94 (1.30 to 6.64)	0.010	2.94 (1.30 to 6.64)	0.010
Bantam	22	281	1.67 (0.87 to 3.19)	0.122	16	117	3.64 (1.81 to 7.34)	<0.001	2.18 (1.21 to 3.93)	0.009
Midget	25	182	1.80 (0.95 to 3.44)	0.073	7	32	2.46 (1.11 to 5.48)	0.027	1.37 (0.73 to 2.55)	0.328
Sensitivity analysis 3.1: imputed participation exposure+raw PA volume
Pee Wee	11	295	1.00 (reference)	NA	11	100	3.14 (1.36 to 7.28)	0.008	3.14 (1.36 to 7.28)	0.008
Bantam	13	165	1.41 (0.68 to 2.94)	0.362	10	74	3.27 (1.44 to 7.43)	0.005	2.33 (1.19 to 4.55)	0.014
Midget	9	110	0.96 (0.44 to 2.07)	0.908	3	23	1.48 (0.36 to 6.10)	0.592	1.54 (0.37 to 6.41)	0.550
Sensitivity analysis 3.2: raw imputed participation exposure+imputed PA volume
Pee Wee	12	376	1.00 (reference)	NA	11	127	2.90 (1.28 to 6.56)	0.010	2.90 (1.28 to 6.56)	0.010
Bantam	22	281	1.64 (0.86 to 3.11)	0.133	16	117	3.67 (1.82 to 7.40)	<0.001	2.24 (1.24 to 4.04)	0.007
Midget	25	182	1.73 (0.91 to 3.30)	0.095	7	32	2.36 (1.06 to 5.25)	0.035	1.37 (0.73 to 2.55)	0.328
Sensitivity analysis 3.3: raw participation exposure+raw PA volume
Pee Wee	11	295	1.00 (reference)	NA	11	100	3.10 (1.34 to 7.19)	0.008	3.10 (1.34 to 7.19)	0.008
Bantam	13	165	1.39 (0.67 to 2.88)	0.383	10	74	3.30 (1.45 to 7.54)	0.005	2.38 (1.21 to 4.70)	0.012
Midget	9	110	0.91 (0.42 to1.99)	0.830	3	23	1.41 (0.34 to 5.82)	0.636	1.53 (0.37 to 6.36)	0.556

Bolded, significant finding (ie, 95% CI do not cross 1.00).
Final model: log odds (number of concussions)=β₀+β₁(PA)+β₂(age group)+β₃(PA×age group), adjusted for clustering by team and offset by participation hours.
IRR, incidence rate ratio; NA, not applicable; PA, physical activity; RR, risk ratio.