Table 1

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

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