The investigators will review video-recordings of three randomized, controlled trials (NCT01535326, 01699399, and 01894191) comparing air insufflation, water immersion and water exchange during colonoscopy. These studies were all conducted at Buddhist Dalin Tzu Chi Hospital.

The investigators will review video-recordings of three randomized controlled trials (NCT01535326, 01699399, and 01894191) comparing air insufflation, water immersion and water exchange. These studies were conducted at Buddhist Dalin Tzu Chi Hospital. Permission will be obtained from the local Institutional Review Board (IRB) to review, analyze and report de-identified findings.

Two experienced endoscopists (YHH and CWT) performed all the recorded colonoscopies. Recordings will be selected for review if they are complete examinations; include clear identification of the appendiceal orifice and/or the ileocecal valve, indicating arrival at the cecum; available in the appropriate format for video editing; and contain no patient or endoscopist identifiers. Patients with incomplete recordings and a history of bowel resection will be excluded from analysis. The included video recordings will be edited to remove the insertion phase to blind the study reviewer to the insertion techniques. One blinded reviewer uninvolved in the performance of the colonoscopies will be in charge of evaluating the selected videos, using the criteria described by Yung et al

Inclusion Criteria:

• if they are complete examinations; include clear identification of the appendiceal orifice and/or the ileocecal valve, indicating arrival at the cecum; available in the appropriate format for video editing; and contain no patient or endoscopist identifiers.

Exclusion Criteria:

• Patients with incomplete recordings and a history of bowel resection will be excluded from analysis.