Thus the gap between expectations and experience persists during period C. Because her expectations remain unchanged she may have difficulties at work and in relationships with family and friends. During a chronic episode of back pain ( b) the woman may believe that at her age she should have no pain. The model shows a number of possible trajectories in illness ( a- d). Whenever the experience of health falls short of expectations (after the onset of symptoms at point B) there is an impact (period C). When expectations are matched by current experience, there is no quantifiable impact on quality of life (period A, before the onset of symptoms). It represents the relation between her expectations and her experience of her quality of life. In the figure ( a) shows a model of an acute episode of back pain occurring in a 35 year old woman over time (A-D). Considering quality of life as the discrepancy between our expectations and our experience provides a way of explaining how we evaluate it. 3 Therefore the relation between symptoms and quality of life is neither simple nor direct. Yet patients with severe disease do not necessarily report having a poor quality of life. Understanding the mechanisms through which health, illness, and healthcare interventions influence the quality of life (that is, understanding the determinants of quality of life) may highlight ways in which it can be maximised.ДЄ primary aim of treatment, particularly in chronic disease, is to enhance the quality of life by reducing the impact of the disease. However, the measures do not consider how people arrive at these judgments. Quality of life is a broader concept and is concerned with whether disease or impairment limits a person's ability to fulfil a normal role (for example, whether the inability to climb stairs limits a person at work).

This is what distinguishes them from measures of disability that ask about an ability to complete specific tasks, such as climbing stairs or dressing oneself. Measures of the quality of life summarise the judgments people make to describe their experiences of health and illness. The implications of these concepts for the use of quality of life as an indicator of the need for treatment and as an outcome of care are discussed.Дefinitions and determinants of quality of life

We propose a model of the relation between expectations and experience and use it to illustrate problems in measuring quality of life. People assess their health related quality of life by comparing their expectations with their experience. We contend that perceptions of health and its meaning vary between individuals and within an individual over time. The central concern of this paper is the tendency to regard the quality of life as a constant. 2 This article assumes it to be those aspects of an individual's subjective experience that relate both directly and indirectly to health, disease, disability, and impairment. Definitions range from those with a holistic emphasis on the social, emotional, and physical wellbeing of patients after treatment 1 to those that describe the impact of a person's health on his or her ability to lead a fulfilling life. There is no consensus on the definition of quality of life as it is affected by health (health related quality of life). For these reasons, the quality, effectiveness, and efficiency of health care are often evaluated by their impact on a patient's вЂњquality of life.вЂќ The two factors driving this change are the recognition of the importance of the social consequences of disease and the acknowledgement that medical interventions aim to increase the length and quality of survival.

The way we think about health and health care is changing.