|Description of comorbidity measures|
|Measure||Definition||Data Source||Variable Categories for the Predictive Modela|
|Number of diagnoses||Identifies number of diagnosis codes, to the third digit. Minimum score is 0 and there is no maximum||Hospital records and physician billing claims||0−2 (reference), 3–5, 6–9, 10 or more|
|Charlson index||Summarizes diagnoses for 17 conditions. Total score can range from 0 to 32||Hospital records and physician billing claims||0−1 (reference), 2–3, 4–5, 6 or more|
|Elixhauser index||Captures diagnoses for 31 conditions. No total score is produced||Hospital records and physician billing claims||Dummy variables (0 = absent; 1 = present) are used to define the 31 conditions|
|Number of drugs||Identifies number of prescription drugs using six-digit AHFS codes. Total score can range from 0 to 125||Prescription drug records||0−1 (reference), 2–3, 4–5, 6 or more|
|Chronic Disease Score (CDS)||Uses AHFS codes to identify number of different prescriptions for treating 17 conditions. Total score can range from 0 to 35||Prescription drug records||0−1 (reference), 2–3, 4–5, 6–7, 8 or more|
aVariable categories were defined based on previous research and by examining the frequency distributions for each of the comorbidity measures. Cut-points for the categories were created to minimize sparse cell sizes, AHFS American Hospital Formulary System.
Lix et al.
Lix et al. BMC Health Services Research 2013 13:340 doi:10.1186/1472-6963-13-340