[Quality of life research methodology].

An elaborated research methodology elucidating the scientific quality of health-related quality of life questionnaires has been developed. With the availability of a methodology that can investigate important aspects of the validity and reliability of questionnaires, the central question is no longer whether questionnaire based studies are valid, but to what extent their validity in specific applications has been sufficiently researched. Newer statistical methods will facilitate a shift towards interactive, individualized questionnaires.