Effective bowel preparation is important for examination of the entire colon adequately and for identifying colonic lesions during colonoscopy. However, it is well known that bowel preparation of inpatients is much poorer than that of outpatients. Our goal is to improve bowel preparations with reinforcement of nurse education that explains the steps required for bowel preparation for inpatients undergoing colonoscopies. The education will focus on explaining the purpose of a screening colonoscopy, the rationale for bowel preparation, the pre-colonoscopy diet, and the instructions for completing the laxative. Patients in the control group will receive the standard written bowel preparation instructions, while patients in the intervention group will receive standard written instructions plus a explanation from reinforcement-educated nurse. The investigators hypothesize that patients received a explanation from reinforcement-educated nurses will lead to improved patient compliance and a better bowel preparation. In addition, the investigators hypothesize that a better quality bowel preparation will improve detection of colonic polyps and patients' satisfaction for colonoscopy.