The NICE experience of designing and utilising severity weights.

Background: In January 2022, NICE changed from "End of Life" (EoL) to "severity" weights, whereby additional value is applied within cost effectiveness analysis to health benefits arising from health technologies deemed to qualify This study examines the relationship between these concepts, how they relate to patient age, and whether the new system is cost-neutral as intended. Methods: Data was extracted from 555 NICE Technology Appraisal decisions from 2009 to 2024. Absolute (AS) and proportional shortfall (PS) severity indicators were estimated for pre 2022 decisions. Post 2022 decisions were judged against EoL criteria.We describe the relationship between severity weights, including the constituent AS and PS elements, age and EoL. Comparisons are made between the distribution of AS, PS and overall severity categories using descriptive statistics and significance tests. Results: AS and PS have different relationships with patient age. In NICE appraisals, AS reduces with age but the relationship is flat between 40 and 60 years. All decisions in the highest AS category (AS > 18 QALYs) have a starting age below 20 years. PS peaks around 60 years. EoL applies almost exclusively where age exceeds 40 years. 91 % of appraisal decisions meeting EoL would receive a severity weight above 1.There is no difference in the mean severity weight between pre and post 2022 appraisal decisions (1.116 vs 1.125). Mean AS is lower in post 2022 appraisals. Conclusions: Severity weights do not correlate precisely with EoL. They have been applied as often as expected. The change from EoL to severity weights has been approximately cost-neutral.