Health-Related Quality of Life Models: Systematic Review of the Literature

Purpose: This review evaluates howtheory-driven models of health-related qualityof life (QoL) take into account themethodological and conceptual problemsbesetting the field. Methodology: 68 modelsformulated from 1965 to 2001 (60% of thosefound for each decade) were randomly selected.Two judges evaluated the models using ananalysis grid covering a) the models' level ofconceptualization (from less to moresophisticated); b) the definition of QoL; c)the distinction between factors that mayinfluence QoL and QoL per se; and d) thepresence of instruments as tools to measureQoL. A global score reflecting the overallquality of the models was also provided.Results: Of the 68 theory-driven modelssampled, approximately 35% were in the lesscomplex category, 15% were in the mostsophisticated group and nearly 50% were inbetween. QoL was not defined by at least 25%of authors. The distinction between factorsthat may influence QoL and QoL per se wasmade in less than 50% of models. Instrumentsused were identified by 78% of authors. Lessthan 3% of the models examined received themaximum global score. Conclusions: From 1965 to2001, a general improvement in the quality ofQoL models is identified. However, for manymodels, the questions used to analyze modelswere not always clearly addressed (many did noteven define QoL), rendering analysis quitedifficult. Overall, the field needs moresophisticated models and a better definition ofthe content and boundaries of the QoL concept.