Accurate optical diagnosis of colorectal polyps could allow a "resect and discard" strategy with surveillance intervals determined based on the results of the optical biopsy. The investigators perform education to characterize the histology of diminutive and small colorectal polyps by using narrow band imaging (NBI). After education program, the investigators prospectively evaluate real-time optical biopsy analysis of polyps with NBI by 15 gastroenterologists at a medical check up center.

This study is an extension of quality assurance program in Seoul National University Hospital Healthcare System Gangnam Center. This study is composed of four periods.

First, a computer based education program on the accuracy of predicting polyp histology with NBI (NICE and WASP classification) will be performed by 15 endoscopists (less experienced in NBI) during Septepber 2015.

In the second period from October 2015 till Deceber 2015, 1st phase real- time optical diagnosis for diminutive and small colorectal polyps will be activated. All endoscopists will have weekly feedback on their accuracy of optical diagnosis for polyps, and discuss the NBI findings that mismatched by histologic diagnosis all together per one month.

Third, the result of 1st phase real-time optical diagnosis will be analyzed from January 2016 till April 2016. In this period, endoscopists with low accuracy of 1st phase real-time optical diagnosis will be re-educated.

The last period from May 2016 till September 2016, 2nd phase real-time optical diagnosis for polyps will be activated. Performance will be evaluated by comparing optically predicted diagnosis with actual histologic diagnosis. Cumulative sum analysis will be used to determine the learning curve for each endoscopist. Negative predictive value for the prediction of nonneoplastic polyp and concordance of surveillance intervals for diminutive polyps diagnosed optically with high confidence will also be measured.

Inclusion Criteria:

• Customers who received screening and surveillance colonoscopy in Seoul National University Hospital Healthcare System Gangnam Center from October 2015 to September 2016.

Exclusion Criteria:

• Age <18 years
• Customers who refused to offer their health check up data
• History of inflammatory bowel disease
• History of familial adenomatous polyposis
• Customers who received Incomplete colonoscopy
• History of previous colorectal resection
• Incomplete data collection on optical diagnosis

Customers who received colonoscopy for screening and surveillance of colorectal neoplasia in Seoul National University Hospital Healthcare System Gangnam Center from October 2015 to September 2016.