This helpful table from Appendix D (page 127) of the BPG Delirium, Dementia and Depression in Older Adults: Assessment and Care (2016) helps to distinguish among delirium, dementia and depression where features are often similar or overlapping.
Registered Nurses’ Association of Ontario. (2016). Delirium, Dementia, and Depression in Older Adults: Assessment and Care. Toronto, ON, Canada: Author. Retrieved from http://rnao.ca/bpg/guidelines/assessment-and-care-older-adults-delirium-...