Table 2

Study characteristics

StudyStudy designLength of exposureStudy populationAge
(years)
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
11–12
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)
Bantam
13–14
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.