Projecting delay and compression of mortality

Abstract Background Although mortality delay (the shift of the age-at-death distribution to older ages) and mortality compression (less variability in the age at death) are the key dynamics that drove past mortality trends, they have seldom been included in mortality projections. Objective We compare the projections of a new parametric mortality model that captures delay and compression of mortality (CoDe) with projections based on the well-known Lee-Carter (LC) model. Data and methods We compare the two models’ properties and in-sample and out-of-sample performance using data from 1960 to 2014 for French, Japanese, and American women and men. Results The CoDe model has less parameters to describe the shape of the age pattern, but more parameters to describe the changes in the age pattern, provides extrapolation to higher ages, allows to estimate the modal age at death, does not assume the exponential decline of rates across all ages, decomposes the delay and compression effect, and can serve as a diagnostic tool. While the LC model provides a better fit at younger ages, the CoDe model provides a better fit at older ages. The LC model consistently projects a slowdown of mortality delay and thus of the increase in life expectancy at birth, whereas the CoDe model can project a continuation of delay and thus a steady increase in life expectancy. Conclusion Projecting mortality by including mortality delay and compression can result in better forecast performance than using the LC model, especially when the modal age at death increases linearly