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

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.