Assessing symptoms, disease severity, and quality of life in the clinical context: a theoretical framework.

Health-related quality-of-life instruments can yield important health information that is often distinct from objective measures of symptoms and disease severity that clinicians are most attuned to. Comprehensive health assessment can be difficult because there are many available measurement instruments that vary in their scope and content. The conceptual boundaries between symptom, disease severity, and health-related quality-of-life instruments are frequently blurred in practice, and what is measured may not coincide with clinical and research goals. The Assessing the Impact of Disease framework aims to clarify the process of selecting appropriate assessment instruments. Three common diseases are discussed in depth to illustrate the applicability of Assessing the Impact of Disease in distinguishing between symptom, severity, and health-related quality-of-life measurements.