Aspects of the present disclosure involve a system comprising a computer-readable storage medium storing a program and method for determining zone identification reliability. The program and method provide for receiving plural page samples of a webpage or page group, each page sample of the plural page samples corresponding to a respective pageview of the webpage or page group; determining, for each page sample of the plural page samples, zone identification information for the page sample, the zone identification information indicating targets and zones identified by the targets for the page sample; detecting any identification errors with respect to the zone identification information for the plural page samples; and determining, based on the detecting, a reliability of the zone identification information.