[Assessment of quality of life in health services research - conceptual, methodological and structural prerequisites].

On July 1, 2009, the German Network for Health Services Research [Deutsches Netzwerk Versorgungsforschung e. V. (DNVF e. V.)] approved the Memorandum III "Methods for Health Services Research", supported by the member societies mentioned as authors and published in this Journal [Gesundheitswesen 2009; 71: 505-510]. This is an in-depth publication on "quality-of-life assessment in health services research". Within the context of the health sciences, quality of life (QL) encompasses the subjective well-being and functioning in the physical, psychological and social domains. QL informs about the aspects of health care that "actually get to the patient". QL is what patients primarily experience, what they talk about and what to a large degree affects the acceptance of health-care services and processes in the society. Therefore, QL can be considered as a highly important endpoint within health services research. The importance of the construct quality of life is also emphasised in German treaties on social law and utility analyses. This paper is the first account on the relations between health services research and the concept and assessment of QL. Our working group has specified key criteria for QL assessment within studies on health services research. (1) Assessment instruments need to comply with standard quality criteria (reliability, validity, sensitivity, interpretability) and the decision for a particular instrument has to be reasonably justified. (2) Study design and study population have to match with the scientific research question and the sample size has to be biometrically sound. (3) QL assessment including time points over the course of the study has to follow a standardized protocol. (4) Criteria for analysis and interpretation have to be prospectively specified. (5) Studies focusing on diagnostic/therapeutic issues need to specify standards for diagnostic criteria and related therapeutic interventions.