3.1 - The Clustering Effect on Defect Level Modeling Authors: Jose T. de Sousa Univ/Comp: Bell Labs. Presenter: Jose T. de Sousa - sousa@research.bell-labs.com ******** Abstract: A defect level (DL) model that considers the clustering effect is proposed. It uses negative binomial statistics, completely unifying yield (Y) and DL theories. It is well known that the clustering effect produces significantly more optimistic yield estimates. This paper shows that clustering also produces significantly more optimistic DL estimates. This is one of the important factors that explain why in reality the defect coverage requirement is significantly less stringent than predicted by some of the previous models.