Re-classification and Weighting of Multiple Causes of Death: US Death Certificates 2003–2023

Abstract Death certificates record causes of death as reported by certifiers (Entity Axis) and as standardized by mortality coding rules (Record Axis). Conventional mortality statistics then reduce these to a single underlying cause, ignoring other contributing conditions; weighting schemes can instead distribute the mortality burden across all listed causes. We evaluated the impact of re-classification from Entity to Record axis and weighting across all 56,986,831 US death certificates from 2003–2023, mapping ICD-10 codes to 14 broad disease categories and testing three weighting schemes: W1 (50% weight to the underlying cause, 50% shared equally among contributing causes), W2 (equal weighting across all causes), and W2A (equal weighting at the ICD-10 code level). Entity and Record Axes agreed on underlying cause in 48,313,403 deaths (84.8%) by broad disease category and in 39,260,709 deaths (68.9%) by ICD-10 code (Supplementary Tables S5A, S5B); concordance reached 70.4% when using 3-character rather than 4-character ICD-10 categories. Re-classification markedly increased COVID-19 deaths (+92%) and Transport deaths (+43%) while markedly decreasing Other External Causes (-54%). Weighting substantially altered death burden attribution: COVID-19 (−44–63%) and Falls (−46–66%) decreased, Other External causes more than tripled (+204–254%), and deviations from unweighted counts were more pronounced with W2 and W2A than with W1. Weighting also brought disease-category counts closer to Entity Axis values and restored Respiratory seasonality patterns suppressed during the pandemic years. Systematic differences between reported and re-classified causes of death, and the choice of weighting scheme, profoundly alter disease burden estimates for several causes, with major implications for resource allocation and public health priorities. SIGNIFICANCE STATEMENT Standardized re-classification processes using mortality coding rules recast the selected causes of death in many death certificates. Moreover, vital statistics typically isolate a single underlying cause, while for many deaths multiple causes jointly lead to demise. Analysis of ∼57 million deaths in the USA (2003-2023) shows that a large proportion of deaths are re-classified by rules to different causes than those filled by original certifiers. Analyses that give weight not only to recorded underlying cause but also to other listed causes lead to markedly different estimates of deaths from several diseases. For example, the footprint of COVID-19 fatalities during the pandemic years decreases by 44-63%. Re-classification and weighting schemes may have profound impact on disease burden estimates and policy decisions.