Accurate optical diagnosis of colorectal polyps could allow a "resect and discard" strategy based on the results of the optical biopsy. Even though intensive training for optical diagnosis, there is still wide variability in individual endoscopists to meet the PIVI thresholds. The investigators with experience of prior optical diagnosis training perform new education and drill to apply proper high confidence according to their decision time. After the education program, the investigators prospectively evaluate real-time optical biopsy analysis of polyps in 8 academic gastroenterologists.

This study is an extension of the Gangnam-READI program (NCT02516748) in Seoul National University Hospital Healthcare System Gangnam Center. This study is composed of two periods. First, an education program on predicting polyp histology and real-time optical diagnosis will be performed by 8 endoscopists From February to March 2020. In the second period from April 2020 till October 2020(total 6 months), real-time optical diagnosis with time drill for diminutive and small colorectal polyps will be activated. Endoscopists will have 3 seconds rule to make high confidence diagnosis and have feedbacks on their accuracy of optical diagnosis for polyps per 3 months. The performance will be evaluated by comparing the optically predicted diagnosis with the actual histologic diagnosis. Negative predictive value for the prediction of non-neoplastic polyp and concordance of surveillance intervals for diminutive polyps diagnosed optically with high confidence will be measured. In addition, the characteristics of the endoscopist affecting the performance of optical diagnosis were investigated.

Inclusion Criteria:

1. Board-certified gastroenterologists
2. Endoscopists who finished ex-vivo optical diagnosis training

Exclusion Criteria:

1. Inflammatory bowel disease
2. Previous colon cancer history
3. Previous colon op. history
4. Melanosis coli