Data were abstracted from the APACHE III database using appropriate software (Cerner Corporation; Kansas City, MO). These data had been collected prospectively. The APACHE III prognostic system calculates the probability of hospital death based on operative status, chronic health condition, admission diagnosis, age, pulse rate, mean arterial BP, temperature, respiratory rate, arterial oxygen tension, hematocrit, WBC count, creatinine level, urine output, levels of BUN, sodium, albumin, bilirubin, and glucose, acid-base status, and neurologic status. The data collected included age, ethnicity, gender, ICU admission date and time, ICU admission source, ICU admission type (postoperative or nonoperative), intensity of treatment, ICU admission diagnosis group, APACHE III score and predicted hospital mortality, and hospital discharge status. The admission sources were categorized as operating room/recovery room, emergency department/direct admission from outpatient clinic, transfer from the same hospital, and transfer from other institutions. The intensity of treatment was divided into the following three categories: “active treatment,” if a patient received ≥ 1 of 33 items of the therapeutic intervention scoring system78 that were defined as ICU-specific therapy on the first ICU day; “high-risk monitor,” if a patient who had not received active treatment on the first ICU day had a > 10% probability of receiving active treatment during the ICU stay; and “low-risk monitor,” if a patient who had not received active treatment on the first ICU day had a < 10% probability of receiving active treatment during the ICU stay.9 Examples of the 33 active treatment items include controlled ventilation, tracheal intubation, cardiac pacing, intraaortic balloon assist, vasoactive drug infusion, hemodialysis, emergency endoscopy, ventriculostomy, and induced hypothermia.910 The ICU admission diagnosis groups included cardiovascular, genitourinary, GI, hematologic, metabolic/endocrine, musculoskeletal/skin, neurologic, respiratory, transplant, and trauma. APACHE III scores and predicted hospital mortality rates were calculated as described by Knaus et al.11 The type of ICU that each patient was admitted to was recorded.