Community-based studies of Alzheimer's disease: statistical challenges in design and analysis.

Alzheimer's disease is a chronic disease, primarily of the elderly, characterized by progressive dementia and eventual death. Community-based studies will likely provide a better representation of the spectrum of disease than will studies drawn solely from clinical sources, because an unknown and possibly substantial fraction of the cases do not come to the attention of the medical care system, or are diagnosed only very late in the disease. Community-based studies will provide not only more accurate estimates of prevalence and incidence, but also more directly comparable unaffected people for studies of risk factors for onset and progression. Such studies are likely to consist of a census component where relatively inexpensive but useful auxiliary information is collected and a probability sample from the census, with the detailed and costly clinical diagnosis of Alzheimer's disease restricted to the sample. The statistician faces challenges both in designing a sample that meets multiple objectives efficiently and in analysing data from the resulting complex survey designs.