The three-phase model is an important orientation framework in the diagnosis of dementia diseases that helps to classify the progressive symptoms according to their severity. This involves looking not only at internal symptoms, but also at external factors that affect a self-determined lifestyle or the ability to cope with everyday life independently. 

Hans Förstl and Christoph Lang present a classification according to the severity of a dementia syndrome based on the 10th revision of the International Classification of Diseases (ICD-10) in the following table:

Degrees of severity of a dementia syndrome according to ICD-10