  The Lee Carter modelling framework is widely used because of its simplicity
and robustness despite its inability to model specific cohort effects. A large
number of extensions have been proposed that model cohort effects but there is
no consensus. It is difficult to simultaneously account for cohort effects and
age-adjusted improvements and we here test a simple model that accounts for
both: we simply add a non age-adjusted cohort component to the Lee Carter
framework. This is a trade-off between accuracy and robustness but, for various
countries present in the Human Mortality Database and compared to various
models, the model accurately fits past mortality data and gives good
backtesting projections.
