CMI Working Paper 217

CMI Working Paper 217 was published in November 2026. The working paper presents the results of an analysis of the seasonality of the SAPS dataset. It is the first analysis of its kind from the SAPS Committee. This paper analyses both the “total dataset” and the “IMD dataset” as described in Working Paper 209. 

To analyse the seasonality of the SAPS dataset, we calculate the 100 Actual/Expected (100 A/E) results and Age-Standardised Mortality Rates (ASMRs) for calendar months over the period 2017-2024. We also include a numerical “Seasonality Ratio” alongside monthly results. This considers the average A/E in the winter months compared to the average A/E in the summer months. The working paper also compares seasonal experience in the SAPS dataset with experience in the general population of England and Wales over the same period.

The analysis shows that:

• Experience by month
  • Experience was notably heavy in March, April and May 2020, and April 2020 was the heaviest month in the eight-year investigation period. Experience in late 2020 and the first quarter of 2021 was also heavier than normal, due to the impact of the COVID-19 pandemic. 
  • The 2017-2018 winter (i.e. December 2017 to February 2018) and 2022-2023 winter are heavier than other winters (excluding the periods affected by the COVID-19 pandemic). This is consistent with data published for the UK general population, which experienced a much higher number of influenza-associated deaths in these winters. 
• Granular experience by month
  • The experience of the oldest age band (86 to 95) was most heavily influenced by the seasonal nature of mortality. 
  • Male and female pensioners in the highest pension amount bands have the lowest Seasonality Ratios, and individuals living in the most affluent IMD deciles have the lowest Seasonality Ratios. 
• Comparison to the general population 
  • In all years, male pensioners had a higher Seasonality Ratio than males in the England & Wales general population.
  • The patterns for females are less clear, though on average, female pensioners and female dependants have a higher Seasonality Ratio than females in the England & Wales general population.

Summary files of the data

Files used in the analysis are available below. Please note that these files have been made available on the understanding that:

• although the CMI has made reasonable attempts to validate the data, its accuracy cannot be guaranteed and the CMI accepts no liability for its use; and
• any published comment or analysis should acknowledge the CMI as the source of the data.

We have released one output alongside this paper. This is:

• A spreadsheet that includes the data for the charts in the report: “CMI WP217 Chart values v01 2026-11-11.xlsx”. 

Working Paper 217 is available to Authorised Users only.