Patient-related variables associated with underrecognition of delirium by nurses were evaluated. These investigations were performed to determine whether characteristics of the patients, or of the type of delirium, might have made identification of delirium more difficult. Baseline variables examined included patient characteristics such as age, sex, race, educational level, hearing and/or vision impairment, functional disability, cognitive impairment, and illness severity. Cutoff points for variables were selected a priori and based on clinically relevant values or previously published studies. Any activity of daily living impairment was defined as needing physical assistance with at least 1 of 7 basic care skills (ie, feeding, bathing, grooming, dressing, toileting, transferring, or walking) by patient self-report referent to 2 weeks before hospital admission; this cutoff point has been used previously.14,15 Hearing impairment was defined as correctly hearing 6 or fewer of 12 numbers with both ears on the whisper test.23 Vision impairment was defined as corrected binocular near vision worse than 20/70 on the standard bedside Jaeger test.23 Delirium risk group was defined using a previously developed predictive model14 based on 4 risk factors for delirium: vision impairment, severe illness, cognitive impairment, and a high serum urea nitrogen to creatinine ratio. High delirium risk was defined as the presence of 3 or 4 of these risk factors at baseline. Dementia was categorized according to the definition used in previous studies16,24 as (1) a modified Blessed Dementia Rating Scale score greater than 4 or (2) a modified Blessed Dementia Rating Scale score greater than 2 and an MMSE score less than 20 and duration of cognitive symptoms of at least 6 months. To indicate high severity of illness, the cutoff point of greater than 16 was used for the APACHE II index.14,25 One postbaseline variable, the presence of hypoactive delirium, was examined for its association with underrecognition by nurses. Hypoactive delirium was defined as the presence of delirium with psychomotor retardation, characterized by an unusually decreased level of motor activity, such as sluggishness, staring into space, staying in one position for a long time, or moving extremely slowly. Although different pathogenic mechanisms for delirium (eg, infection, medications, and metabolic derangements) may have the potential to affect recognition of delirium, exploration of these myriad factors was beyond the scope of the present study.