What are quality of life measurements measuring?

It is now widely acknowledged that the personal burden of illness cannot be described fully by measures of disease status such as size of infarction, tumour load, and forced expiratory volume. Psychosocial factors such as pain, apprehension, restricted mobility and other functional impairments, difficulty fulfilling personal and family responsibilities, financial burden, and diminished cognition must also be encompassed. The area of research that has resulted from this recognition is termed âhealth related quality of life.â It moves beyond direct manifestations of illness to study the patient's personal morbidityâthat is, the various effects that illnesses and treatments have on daily life and life satisfaction. Although quality of life assessment was almost unknown 15 years ago, it has rapidly become an integral variable of outcome in clinical research; over 1000 new articles each year are indexed under âquality of life.â Although the importance of quality of life is broadly acknowledged, scepticism and confusion remain about how quality of life should be measured and its usefulness in medical research. These responses may reflect important conceptual and methodological limitations of the current concept of quality of life. We offer a simple framework that describes the core elements of quality of life related to health and use this to evaluate quality of life measurement as it is currently conducted. Summary points Measures of disease status alone are insufficient to describe the burden of illness; quality of life factors such as pain, apprehension, depressed mood, and functional impairment must also be considered Two operational definitions of quality of life are identifiedâobjective functioning and subjective wellbeing Assessments of objective functioning and subjective wellbeing convey different information, they also present different problems in relation to validation Assessment of functioning derived from questionnaires must be validated against measures of directly observed behavioural performance Subjective appraisal of wellbeing may be influenced substantially by psychological factors unrelated to health or to changes over time in patients ' criteria for appraising wellbeing Whether and how quality of life researchers respond to these obstacles and deficiencies will probably determine the quality of their work in the future. © 1998, BMJ Publishing Group Ltd. All rights reserved.