The hierarchy of quality-of-life assessment, the Health Assessment Questionnaire (HAQ), and issues mandating development of a toxicity index.

Health, as defined by the World Health Organization, encompasses the more redundant and cumbersome phrase "health-related quality of life." Valuations by patients naturally separate this entity into the primary dimensions of absence of death, disability, discomfort, drug toxicity, and destitution. These dimensions separate naturally into subdimensions, and the subdimensions into components, thus providing a hierarchy under which assessment of particular aspects of health may be placed. In the clinical trial situation, it is essential that all dimensions always be assessed and reported, because otherwise, misleading conclusions may be drawn. On the other hand, it is much less important which assessment instrument is chosen, or how much detail is assessed for each dimension. The Health Assessment Questionnaire (HAQ) has been developed under a hierarchical conceptual model and widely used; its characteristics are described. A new index for measurement of drug toxicity has been developed for the HAQ, and its crucial role in comparing treatments in a clinical trial discussed. Issues in reliably describing comparative drug toxicity are developed, a toxicity index presented, and some preliminary results and conclusions outlined. With the ability to quantitatively describe drug toxicity, health assessment becomes conceptually more complete.