Quality of life in psychiatry: a systematic contribution to construct validation and the development of the integrative assessment tool "modular system for quality of life".

The aim of the present study is to contribute to an ongoing validation process of the Quality of Life (QoL) construct in the clinical field by investigating its internal structure. Eight (inter)nationally validated questionnaires have been analyzed by an integrative approach in a multicenter study. Data has been collected in a mentally healthy (n = 479), a depressed (n = 171) and a schizophrenic (n = 139) sample. Apart from conventional psychometric criteria a similarity structure analysis (SSA) within a facet analytic methodology has been applied. A dimensional structure of the resulting integrative questionnaire "Modular System for Quality of Life" (MSQoL) could be generated that consists of one "G-factor" (life in general) and six specific dimensions (physical health, vitality, psychosocial relationships, material resources, affect, leisure time). This basic structure represents a core module measured by 47 items which is sufficiently valid for all three samples. The empirical structures of healthy, depressed and schizophrenic samples fulfill the first law of attitude and share a common variance of 95%. In addition, there are four specific modules (demography, family, partnership, profession). No specific modules could be identified for the psychopathological subgroups. The conclusion can be drawn that QoL is construed very similar by all three investigated populations which is the base for searching for quantitative differences and profiles. The MSQoL integrates the non-redundant components of eight QoL-instruments, is psychometrically able to assess the basic structure and can be completed within a cumulative research design by items specific for a particular setting.