Alzheimer ’ s disease 49 4 Alzheimer ’ s disease

(a) The types of population vary enormously in parameters such as place of residence (e.g. community versus hospital-based samples) and age range (as dementia is much more common in the very elderly, a sample stratified towards the upper age ranges will contain numerically more cases). (b) The diagnostic procedures vary, some involve personal examination by trained staff, others rely on second-hand information. (c) The use of ancillary investigations and diagnostic categories vary. (d) Many reports simply talk of cognitive impairment, some diagnose dementia, but relatively few attempt accurate subtyping of cases into Alzheimer’s disease or vascular dementia.