The proposed Phase B studies will be carried out in hospitalised patients in general and acute medical wards and ICU. The objectives of these studies are (a) to assess diagnostic performance of the DelApp in discrete patient groups and to inform optimal cut-points (Phase B); and (b) to evaluate the diagnostic performance of the DelApp in unselected patients (Phase C). The studies will also contribute to a better understanding of the nature of neuropsychological deficits underlying delirium. At the end of these studies, the DelApp may be modified depending on the study results. Investigators will select the stimuli and subtests that provide the best balance of sensitivity and specificity.