CMI Working Paper 116

The value of the period smoothing parameter, S_k, in CMI_2018

Following consultation in CMI Working Paper 114, the Mortality Projections Committee confirms that it will change the Core value of the period smoothing parameter, S_k, to 7 in CMI_2018. This parameter determines how responsive the Model is to recent data and has particular significance given the stark reduction in mortality improvements in England and Wales’ population data that took place around 2011.

In response to the consultation, we intend to add a new input to CMI_2018, an addition to the age-period component of initial mortality improvements. This will enable users to reflect historical differences in mortality improvements between populations, without needing to modify, S_k.

CMI Working Paper 116 summarises responses to the consultation, and discusses our decisions.