Longitudinal studies of cognitive, functional and behavioural change in patients with Alzheimer's disease

This paper reviews data on the natural history of symptoms in patients with Alzheimer's disease (AD) and describes some of the problems encountered in analysing longitudinal data in this population. Data on cognition, functio nal ability and psychiatric or behavioural symptoms have all been obtained from AD patients. Because of attrition, the length of follow-up is not unif orm for all patients and neither is the frequency of evaluation, Furthermor e, patients enter longitudinal studies with a wide range of symptom severit y and longitudinal decline in cognition and function is distinctly non-line ar. Behavioural symptoms do not progress regularly in AD but are episodic p henomena not closely related to cognition or function. Strengths and limita tions of various analytic techniques used for hypothesis testing with these longitudinal data are described. Copyright (C) 2000 John Wiley & Sons, Ltd .