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Medical care aims not only to cure disease, or lengthen survival,
but also to improve all the dimensions of health-related quality
of life. Symptoms of disease or its treatment are an important
dimension of health-related quality of life, specifically in advanced
disease, and in palliative care, where the emphasis is on helping
those affected by progressive illness live as well as possible
until they die, and on improving the quality of death. In such
circumstances, symptoms are complex, often multiple, and increase
in severity and frequency as the disease progresses. Although
clinical symptoms are only one component affecting quality of
life, a high level of symptom-related distress can impair all
the other quality of life dimensions. Consequently, not treating
them adequately will significantly impair a patient's quality
of life and increase the family's suffering.
In contrast
to what is known about survival and its determinants, very little
is known about the natural history, determinants, and interactions
of symptoms in patients with advanced disease. For example, estimates
on expected survival are available for all stages of the most
common diseases (either as probability of survival, or as median
survival). But information about what a patient can expect in
terms of symptom distress during the advanced phase of disease
is usually less reliable and often lacking. A better understanding
of the epidemiology of symptoms in advanced disease might improve
the patient/clinician relationship by providing the professional
with more information about expected patient quality of life.
This information is crucial for identifying symptoms that are
more likely to afflict patients. The information can also be used
to plan clinical studies aimed at identifying more effective treatments.
The study
of both survival and symptoms requires valid methods of study
design and analysis that address such issues as bias and confounding
factors. When studying survival, measurement is fairly straightforward
-- it requires identifying when people die, and when the disease
began. However, the measurement of symptoms is complex, and needs
to take into account issues of definition, detection, and variation
over time. This chapter considers measurement and study design,
and is relevant to all types of studies assessing symptoms.
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