data item adverse event relative risk YH a data item that represents the ratio of the rate of occurence of the adverse event in persons having the medical intervention (e.g., vaccination) to the rate in otherwise comparable persons without the medical intervention. Stratton KR, Howe CJ, Johnson RB. 1994. Adverse events associated with childhood vaccines: Evidence bearing on causality. National Academy Press. Washing, D.C. Page 20-21.