Calculating measures of comorbidity using administrative data

The development of a Stata program to calculate published measures of comorbidity will be of value to researchers working with inpatient discharge data coded in ICD-9-CM or ICD-10. The comorbid command calculates the weighted sum of comorbidities, as well as comorbidity scores based on the Charlson Index, which reflects the cumulative increase in likelihood of 1-year mortality from comorbidities. This allows for the calculation of three different comorbidity measures: ICD-9-CM, Enhanced ICD-9-CM, or ICD-10 (Quan et al 2005). Exclusion of less severe comorbidities can occur using an optional hierarchical method that excludes from the calculations a mild comorbidity when a patient has also exhibited a more severe form of the same diagnosis. The comparable elixhauser command calculates the sum of this alternate set of comorbidity measures, which may be associated with negative hospital outcomes (Elixhauser et al 1998). Both Stata algorithms can handle patients or visits as the observational unit. Options allow for a choice of summary output.

Additional information
Stagg_Stata_Presentation_final (slides) 
stagg_notes_final (presentation notes)