This paper discusses a new pattern of mortality model which is built on the form and
knowledge of the two-factor mortality model named after its designers Cairns, Blake and
Dowd (2006). This model – the CBD model – is widely used and has been extended by the
authors in a number of ways, including by the use of a cohort effect. In this paper, we
propose a range of new parsimonious approaches to model the cohort effect. Instead of
adding a cohort factor to an age-period model we model the effect by building
discontinuities into the pattern of rates within each year. The fit of the resulting models is
close to that available from the best of the CBD derivatives
