Table 2.

Hazard ratios for risk of attention-deficit hyperactivity disorder diagnosis

Age at diagnosis	Mean±SD
Control	17.2±11.7
Concussion	17.8±11.9
Model 1a		Model 1b
HR (95% CI)	P value	HR (95% CI)	P value
1.40 (1.33 to 1.47)	<0.001	1.39 (1.32 to 1.46)	<0.001
Model 2a		Model 2b
1.29 (1.14 to 1.45)	<0.001	1.28 (1.14 to 1.45)	<0.001
Model 3a		Model 3b
1.39 (1.32 to 1.46)	<.001*	1.38 (1.31 to 1.45)	<.001*
1.20 (0.98 to 1.48)	0.08†	1.20 (0.97 to 1.47)	0.09†
0.92 (0.51 to 1.67)	0.78‡	0.94 (0.52 to 1.70)	0.83‡
Model 4a		Model 4b
1.28 (1.21 to 1.35)	<0.001	1.27 (1.21 to 1.34)	<0.001
Model 5a		Model 5b
1.01 (1.00 to 1.02)	0.23	1.01 (1.00 to 1.02)	0.30

Model 1a, Cox proportional HR adjusted for age, sex and geographical location via stratified analysis. Model 1b, model 1a plus adjustment for socioeconomic status and comorbidities. Model 2a, sex-interaction HR adjusted for age, sex and geographical location via stratified analysis. Model 2b, model 2a plus adjustment for socioeconomic status and comorbidities. Model 3a, multiple concussion HR adjusted for age, sex and geographical location via stratified analysis. Model 3b, model 3a plus adjustment for socioeconomic status and comorbidities, Model 4a, control for occurrence of other outcomes of interest between index date and date of outcome of interest in question adjusted for age, sex and geographical location via stratified analysis. Model 4b, model 4a plus adjustment for socioeconomic status and comorbidities. Model 5a, time under study interaction HR adjusted for age, sex and geographical location via stratified analysis. Model 5b, model 5a plus adjustment for socioeconomic status and comorbidities.

For both models 3a and 3b: *HR of 1 concussion vs 0 concussions; †HR of 2 concussions vs 1 concussion; ‡HR of 3+ concussions vs 2 concussions.