Using mortality data to extrapolate the stock of the irregular migrant population

This guide is intended to give an overview of practical steps to be taken to apply mortality-based extrapolation as a means of providing estimates of the size, age structure and (aggregated) national background of “hidden populations”, that is, populations that are present within the national borders of a country a but who are not official residents of that country because they are not captured by population register data or other data (e.g. censuses) relying on an official residence criteria, such as the “usual residence” criterion . The method is composed of two steps: In the first step, an estimate of the population not captured by official data is made, using “unlinked deaths”, i.e. the number of recorded deaths that cannot be matched to a registered resident and expected mortality risks as the basis for the estimate. In a second step, irregular immigrants are identitified, counting all regular status visitors and immigrants and subtracting the aggregated number of regular immigrants from the hidden population estimated in step. In short, the two-step method starts by first making a distinction in terms of registration status (=registered member of official population or not) and only in a second step distinguishing the population in terms of legal status (regular/irregular).