Health-related quality of life models: Systematic review of the literature

Purpose: This review evaluates how theory-driven models of health-related quality of life (QoL) take into account the methodological and conceptual problems besetting the field. Methodology: 68 models formulated from 1965 to 2001 (60% of those found for each decade) were randomly selected. Two judges evaluated the models using an analysis grid covering a) the models' level of conceptualization (from less to more sophisticated); b) the definition of QoL; c) the distinction between factors that may influence QoL and QoL per se; and d) the presence of instruments as tools to measure QoL. A global score reflecting the overall quality of the models was also provided. Results: Of the 68 theory-driven models sampled, approximately 35% were in the less complex category, 15% were in the most sophisticated group and nearly 50% were in between. QoL was not defined by at least 25% of authors. The distinction between factors that may influence QoL and QoL per se was made in less than 50% of models. Instruments used were identified by 78% of authors. Less than 3% of the models examined received the maximum global score. Conclusions: From 1965 to 2001, a general improvement in the quality of QoL models is identified. However, for many models, the questions used to analyze models were not always clearly addressed (many did not even define QoL), rendering analysis quite difficult. Overall, the field needs more sophisticated models and a better definition of the content and boundaries of the QoL concept.