In 1990, the U.S. Census Bureau used a 'capture-recapture' or dual system estimation (DSE) methodology to estimate total population including those missed by the census. The two 'systems' are the census and a Post Enumeration Survey (PES) (Hogan and Wolter 1988). One of the assumptions underlying use of the DSE to estimate population size is that within each poststratum (defined by some set of geographic and demographic variables), being in the census is independent of being in the PES.