As the number of potential therapeutic agents and treatment studies has grown, increasing attention has been given to improving the methodology of clinical trials to assess their efficacy more appropriately. Much of this attention has focused on development and careful consideration of rating scales. A factor in the development of new medications is that the clinical, biological and genetic heterogeneity of Alzheimer's disease, combined with the progressive deteriorating course of the untreated, means that specific treatments will be helpful for only a subset of patients. Some patients will respond dramatically but many more will respond only modestly or not. It is therefore important to be able to assess a range of treatment responses in both individuals and groups of patients, and to identify treatment responders clearly. Furthermore, because dementia affects behavior, physical activities, social functioning, interpersonal relationships, and overall global function, in addition to cognition, clinicians should be able to assess and appreciate improvements in these areas as well. Lastly, it is important that similar ratings are used among the many trials so that clinicians can gain a general appreciation of relative efficacy of medication from study to study and be able to make better comparison between medications.