In his study of Iraq, Roberts divided the country into 33 regions, attempting to sample 30 households for each cluster, and selecting 988 households, with 7868 residents. In September 2004, each surveyed household was interviewed about household composition, births, and deaths since January 2002. Of 78 households where members were asked to show documentation to confirm their claims after the interview was finished, 63 were able to present death certificates.