[Measuring cognitive change in patients with suspected dementia--change norms are lacking for psychometric instruments].

A diagnosis of dementia as well as of mild cognitive impairment requires evidence of cognitive decline over time. Often, cognitive tests are administered to objectively measure cognitive change. However, changes in psychometric test scores do not necessarily result from true cognitive change. They might also be due to chance and to normal variability. This paper discusses why change norms are required for a reasonable interpretation of individual changes in test scores. Norms for change are lacking for most psychometric instruments used for dementia diagnosis in the German-speaking area.