Reclassification and Weighting of Multiple Causes of Death: US Death Certificates 2003-2023

In death certificates Entity Axis reflects reported death causes in their original order, and Record Axis reflects standardized re-classifications processed with expert rules. Additionally, while conventional mortality statistics consider a single underlying cause ignoring multiple contributing conditions, weighting schemes may consider all listed causes. We evaluated the impact of re-classification and weighting schemes across all 56,986,831 US death certificates from 2003-2023. ICD-10 codes were mapped to 14 broad disease categories. We recorded the frequency of changes and concordance in reported underlying cause of death between Entity and Record Axes. We considered weighting schemes for attributing mortality burden with Record Axis data: W1 (50% weight to underlying cause, 50% distributed equally among contributing causes), W2 (equal weighting across all causes) and W2A (equal weighting across all causes at ICD-10 level). Entity and Record Axes agreed on underlying cause category in 84.8% and on specific ICD-10 code in 68.9%. Reclassification from Entity Axis to Record Axis markedly increased COVID-19 (+92%) and Transport (+44%) and markedly decreased deaths from Other External Causes (-54%). Weighting schemes substantially altered death burden attribution: e.g. they reduced COVID-19 (-44-63%) and Falls (-46-66%), and changes tended to be more prominent with W2 and W2A than with W1 weighting. Weighting brought death counts per disease category closer to the Entity Axis. Weighting also restored Respiratory seasonality patterns. Systematic differences between reported and re-classified causes of death and weighting schemes for multiple causes profoundly change some disease burden estimates with major implications for resource allocation and public health priorities. SIGNIFICANCE STATEMENTStandardized re-classification processes using expert 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 expert rules to different causes than those filled by original certifiers. Analyses that give weight not only the recorded underlying cause but also the 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.