Disturbances to health can be divided broadly into limitations of basic activities of daily living (washing, dressing, etc.) that are common to all patients and other limitations that depend on individual circumstances. A distinction should be drawn between health status and health-related quality of life. Health status questionnaires are standardized for "typical patients," and this should be borne in mind when interpreting such scores from studies that give an average result using

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... ased measurements. Such studies give a good indication to payers of the average effects of a treatment, but provide no indication other than probability of benefit to individuals. This applies even more with health improvements that manifest uniquely in each patient. Two widely used disease-specific questionnaires in chronic obstructive pulmonary disease-the Chronic Respiratory Questionnaire and the St. George's Respiratory Questionnaire-are health status, rather than quality of life, instruments. Health status scores from questionnaires provide measures of the effects of disease, not measures of the disease itself. The relationship between high health status score and increased risk of dying is due to the fact that both reflect underlying disease activity. In therapeutic studies, health status improves because the underlying disease activity has been moderated by therapy. Improved health does not improve mortality or morbidity per se. It is also important to appreciate that the impact of any measured change in health may also be determined by the patient's baseline state.