This paper presents a novel system of annual Population Estimates Compiled from Administrative Data Only
(PECADO) for Ireland in the absence of a Central Population Register. The system is entirely based on data
originated from administrative sources, so that population estimates can be produced even without
purposely designed coverage surveys or a periodic census to recalibrate estimates. It requires several
extensions to the traditional Dual System Estimation (DSE) methodology, including a restatement of the
underlying assumptions, a trimmed DSE method for dealing with erroneous enumerations in the
administrative register, and a test for heterogeneous capture probabilities to facilitate the choice of blocking
in applications. The PECADO estimates for years 2011–2016 are compared to the Census counts in 2011
and 2016. We demonstrate how the system can be used to investigate the Census 2016 under-count in
Ireland, in place of the traditional approach of deploying additional population coverage surveys.