<qa>  What is the specific aims of the study?The specific aims are to determine the incidence of medication errors related to antimicrobial prophylaxis for cardiovascular surgery, joint replacement surgery, and hysterectomies across a heterogeneous sample of hospitals; identify organizational and practitioner factors associated with error rates, and evaluate the effectiveness of a multifaceted intervention in reducing prophylaxis error rates compared to written feedback alone in a sample of 44 hospitals enrolled in the study using a rigorous group-randomized design. 