Conceptual, classification or causal: models of health status and health-related quality of life

Instruments intended to assess health-related quality of life (HRQOL) and health status are widely used in research and clinical practice, but with little conceptual guidance there is some uncertainty about what it is that these instruments are actually tapping. Causal models have the potential to provide the required conceptual guidance, not only placing commonly discussed health concepts on a firm scientific foundation, but also allowing medical and psychosocial interventions to be developed in a more focused and efficient manner. Several models, some postulating causal relations, have been proposed over many years, and some have been supported by data. The development and validation of these models has, however, been conducted in a piecemeal fashion. The imperative to develop tailored, cost-effective interventions requires a synthesized approach to developing and testing causal models.