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CMI_2024 consultation

The CMI typically releases an updated version of the CMI Mortality Projections Model each year and we expect to release the next version, CMI_2024, as soon as we are able in Q2 2025 (subject to responses to the consultation). 

This paper consults on our proposed methods and Core parameters for CMI_2024. This follows a wide-ranging review of the Model to address concerns raised over the sustainability of the initial approaches taken as we worked through the aftermath of the pandemic.

As well as the usual updates to the calibration data, we propose to make four changes, described below, to how we calibrate the Model to historical data. 

The two primary changes enable our key aim of better reflecting mortality trends: 

  • extending the existing age-period-cohort improvement (APCI) model to have three period terms, to reflect different trends in mortality at different ages, rather than one as in earlier versions of the Model; and
  • modelling the impact of the COVID-19 pandemic on mortality by adding a “fitted overlay” to the APCI model, rather than using weights as in earlier versions. We use the name “age-period-cohort-overlay improvement” (APCOI) model for the new version of the APCI model which includes the overlay.

The other two changes were not the focus of our review but have proved necessary so that the APCOI model with three period terms and a fitted overlay produces reasonable and reliable results. They also have merit in their own right:

  • applying the existing cohort constraints at low and high ages after fitting the APCOI model, rather than as part of the fitting process, to avoid distorting cohort components at intermediate ages; and
  • changing the algorithm used to fit the APCOI model to be quicker and more robust. 

This paper seeks views of users of the Model on our proposal for CMI_2024. We would like to receive comments by 25 March 2025.

The Committee hosted a webinar on 5 March 2025 providing a summary of the proposals for CMI_2024. A recording of the webinar is now available to view for Authorised Users only.

We have issued illustrative software to accompany the consultation. This incorporates our proposed Core parameterisation, and an indicative dataset for CMI_2024, consistent with Working Paper 197. The software is intended to allow users to better understand the implications of our proposals and assist them in responding to the consultation.

Please note that: 

  • The illustrative software is provided as a “beta” version on an “as is” and “own risk” basis.
  • Results from CMI_2024 may differ from those of the illustrative software. 

We have also issued a spreadsheet showing results for a range of parametrisations and mortality scenarios for potential future versions of the Model to illustrate the options considered in the paper. The spreadsheet includes ASMRs, mortality improvements, life expectancies, and life expectancy changes. 

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