Concussion incidence in the OHL and NHL by season.

Incidence rates were calculated per 100 regular season games. IRRs for concussions and concussions plus suspected concussions were calculated relative to the 2010–11 season. Concussion incidence rate in the NHL was lower in 2009–10 than in 2010–11 (p = 0.002 for concussion and suspected concussion, p = 0.029 for concussion), but there was no significant difference between 2010–11 and 2011–12 (p = 0.727 for concussion and suspected concussion, p = 0.086 for concussion). OHL concussion incidence rates were not different between 2009–10 and 2010–11 (p = 0.074 for concussion and suspected concussion, p = 0.09 for concussion) but concussions and suspected concussion increased from 2010–11 to 2011–12 (p = 0.039, p = 0.483 for concussion only).*indicates p