Gessel, L. M., Fields, S. K., Collins, C. L., Dick, R. W., & Comstock, R. D. (2007). Concussions among United States high school and collegiate athletes. Journal of athletic training, 42(4), S. 495-503. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2140075/

Gessel, Luke M., Sarah K. Fields, Christy L. Collins, Randall W. Dick, and R. Dawn Comstock. "Concussions Among United States High School and Collegiate Athletes." Journal of Athletic Training 42, no. 4 (2007): S. 495-503.

Gessel, Luke M., et al. "Concussions Among United States High School and Collegiate Athletes." Journal of Athletic Training 42.4 (2007): S. 495-503.