“…A similar idea, although differently implemented, was introduced by Li and Lee (2005) in their multi-population extension of the Lee-Carter model. Since Jarner and Kryger (2011), the concept of a reference population has appeared in a number of models and applications, for example Cairns et al (2011), Börger et al (2014, Villegas and Haberman (2014), Wan and Bertschi (2015), Hunt and Blake (2017b), Villegas et al (2017), Menzietti et al, 2019), Li and Liu (2019), .…”