Computing comorbidity indices and scores such as the weighted Charlson score (Charlson, 1987 ) and the Elixhauser comorbidity score (Elixhauser, 1998 ) using ICD-9-CM or ICD-10 codes (Quan, 2005 ). Australian and Swedish modifications of the Charlson Comorbidity Index are available as well (Sundararajan, 2004 and Ludvigsson, 2021 ), together with different weighting algorithms for both the Charlson and Elixhauser comorbidity scores.