Table 2

Study characteristics

StudyStudy designLength of exposureStudy populationAge
Athletes with previous concussion (No)Athletes with no previous concussion (No)Concussion definitionAdjustment factorsEffect estimate
(95% CI)
Zemper, 200340 PCTwo football seasonsNational high school football players (AIMS) (n=7197 player-seasons; male 7197)Not identified2966901AAN 1997N/ARR 6.61 (5.0 to 8.8)
Kontos et al, 200637 PCOne football seasonNew Orleans high school football players (n=158; male 158)14–18
(Mean 15.8±1.2)
29129CISG 2002Learning disability, ADD/ADHD, brain disease or disorder, substance abuseOR 3.71 (1.36 to 10.18)
Chrisman et al, 201935 PC2×10 week football seasonsSeattle youth football league (n=863; male 854)5–7 (n=96)
8–10 (n=300)
11–12 (n=311)
13–14 (156)
115748CISG 2012Age, sex, parent education, ethnicity, race, attention problems, headaches, years playing footballOR 2.24 (1.05 to 4.75)
Tsushima et al, 201836 RCOne school yearMiddle and high-school athletes (n=10 334; male 5938)13 (n=512)
14 (n=2352)
15 (n=2477)
16 (n=2470)
17 (n=1944)
18 (n=579)
17108580CISG 2012Sex, sportRR*
1: 4.34
(3.89 to 4.83)
2: 5.07 (4.37 to 5.88)
3: 3.72 (2.79 to 4.97)
Emery et al, 201038 PCOne ice-hockey seasonAlberta and Quebec Pee Wee ice-hockey players
(n=2154; male 2117)
Sex missing data n=4
Pee Wee
3281786CISG 2004Year of play, player size, level of play, position, body checking attitudeIRR 2.14 (1.28 to 3.55)
Emery et al, 201139 PCOne ice-hockey seasonAlberta and Quebec Bantam ice-hockey players
(n=1971; male 1956)
4531480CISG 2004Clustering by team, year of play, player size, level of play, player position, body checking attitudeIRR 1.87 (1.19 to 2.94)
Black et al, 201634 PCOne ice-hockey seasonAlberta (n=581; male 553) and Ontario (n=280; male 274) Pee Wee non-elite ice hockey players; missing data n=10Pee Wee 11–12138718CISG 2012Clustering by team, exposure hours, year of play, level of play, position, body checking attitudeIRR 3.16 (1.86 to 5.39)
  • *Per previous number of concussions.

  • AAN, American Academy of Neurology; ADD/ADHD, attention-deficit disorder/attention-deficit hyperactivity disorder; AIMS, Athletic Injury Monitoring System; BMI, body mass index; CHOP, Children’s Hospital of Philadelphia; CISG, Concussion in Sport Group; IRR, incidence rate ratio; PC, prospective cohort; RC, retrospective cohort; RR, rate ratio.