Terms to describe the behavioral and psychological symptoms commonly seen in dementia, including “Behavioral and Psychological Symptoms of Dementia” (BPSD), “non-cognitive symptoms,” and “neuropsychiatric symptoms,” were introduced in the 1980s and 1990s to draw attention to the heterogeneous group of symptoms that, distinct from cognitive deficits, are commonly seen in dementia and cause significant distress to patients and carers (Reisberg et al., 1987; Cummings et al., 1994; Allen and Burns, 1995; Finkel et al., 1996). BPSD include a wide range of affective, psychotic, and hyperactivity symptoms, and studies include different combinations of symptoms. These symptoms are also often studied individually outside the context of BPSD in the older population with or without cognitive impairment. Depression is most frequently studied, particularly in the older population without dementia. The relationship between dementia and depression in older people and the courses of the two disorders have been an important research topic for around 70 years (Roth, 1955).