How many polyps are there?

Background Frequently, there is disagreement between consecutive endoscopies about the true number of mucosal lesions. Objective To develop a simple means to estimate the total number of mucosal lesions and the number of lesions missed during consecutive endoscopies. Design Probability modeling of endoscopic outcomes. Patients Subjects undergoing 2 consecutive endoscopies. Main Outcome Measurements Total number of mucosal lesions and number of missed lesions. Results If a represents the number of lesions seen by the first endoscopist, b the number of lesions seen by the second endoscopist, and c the number of identical lesions seen by both, then the total number of lesions is given by T = ab/c, and the number of lesions missed by both is given by M = (a − c)(b − c)/c. The estimated numbers for all lesions and for missed lesions increase as the number of identical lesions seen by both endoscopists decreases. If the number of identical lesions seen by both endoscopists matches the number of lesions found by any one endoscopist, the numbers of estimated and found polyps are identical and the number of missed polyps equals zero. Limitations The analysis assumes that both endoscopists work independently of each other and are equally qualified. The formulas also fail to account for varying characteristics of similar lesions. Conclusion The analysis presents a simple, unbiased means to estimate the total number of mucosal lesions if 2 consecutive endoscopies yield slightly conflicting results. Frequently, there is disagreement between consecutive endoscopies about the true number of mucosal lesions. To develop a simple means to estimate the total number of mucosal lesions and the number of lesions missed during consecutive endoscopies. Probability modeling of endoscopic outcomes. Subjects undergoing 2 consecutive endoscopies. Total number of mucosal lesions and number of missed lesions. If a represents the number of lesions seen by the first endoscopist, b the number of lesions seen by the second endoscopist, and c the number of identical lesions seen by both, then the total number of lesions is given by T = ab/c, and the number of lesions missed by both is given by M = (a − c)(b − c)/c. The estimated numbers for all lesions and for missed lesions increase as the number of identical lesions seen by both endoscopists decreases. If the number of identical lesions seen by both endoscopists matches the number of lesions found by any one endoscopist, the numbers of estimated and found polyps are identical and the number of missed polyps equals zero. The analysis assumes that both endoscopists work independently of each other and are equally qualified. The formulas also fail to account for varying characteristics of similar lesions. The analysis presents a simple, unbiased means to estimate the total number of mucosal lesions if 2 consecutive endoscopies yield slightly conflicting results.