All cases of polypectomy are performed with identical methodology; resection after epinephrine mixture injection under blended or mixed current wave. The data includes the patients information such as sex, age, body weight, BMI and vascular disease history such as hypertension, diabetes, ischemic heart disease, cerebrovascular disease, COPD, modified HAS-BLED score and CHADS2 score. The data of polyp related factor include number of polyps, bleeding status(acute, early, delayed/minimal, moderate, sever), endoscopist (staff or fellow), bowel preparation status, polyp character (shape, location, pathology) and procedures for bleeding (clipping, APC, epinephrine injection, band ligation etc.).