Survival Following a Diagnosis of Alzheimer Disease

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Abstract
LIFE EXPECTANCY following a diagnosis of Alzheimer disease (AD) is important information for health planners, caregivers, patients, and their families. Such information is useful for planning the resources needed for the care of patients with the disease as well as for evaluating the effect on public health and for forecasting the future prevalence of the disease. However, there have been conflicting estimates of the duration of survival following a diagnosis of AD.1-7 A study in 2001 indicated the overall survival of patients with dementia was only 3.3 years.1 As pointed out by Wolfson et al,1 some estimates are biased because they are based on the follow-up of individuals who were found to be prevalent with AD. This can lead to overestimation of survival because persons who die rapidly following a diagnosis of AD are excluded from the study. The resulting bias is called "length" or "survivor" bias, and as described by Wolfson et al,1 a statistical adjustment is necessary to correct the bias.