[Measurement of disease severity in dermatology]

In order to determine the appropriate therapy for dermatological diseases, numerous measurement instruments are available to measure disease severity. Due to the lack of laboratory parameters for some dermatological diseases to objectify the disease severity (e.g., atopic dermatitis, psoriasis), questionnaires are used. Laboratory as well as questionnaire-based measurements should be reliable, valid, and sensitive to change. In addition, measurement instruments should be feasible. Classifications of disease severity which are based on inadequate measurement properties result in incorrect clinical decisions and limit evidence-based healthcare. Therefore, systematically developed and evidence-based recommendations for the use of individual measurement instruments should be taken into consideration.