Table 1.

Definitions of comorbidity groups

Comorbidity group	Comorbid conditions
None	None
Mild	History of myocardial infarction, acute myocardial infarction, ulcer, or rheumatologic disease
Moderate	Cardiovascular disease; paralysis; diabetes; or combinations of diabetes with myocardial infarction, ulcer, or rheumatologic disease
Severe	Acquired immune deficiency syndrome, chronic obstructive pulmonary disease, mild or severe liver disease, chronic renal failure, dementia congestive heart failure, or combinations of conditions not listed above