| |
Measuring symptom
frequency in populations requires the stipulation of diagnostic
criteria. In clinical practice the definition of a "case"
generally assumes that, for any symptom, people are divided into
two discrete classes: the affected and the un-affected.
To define
who has a symptom it is important to use a valid and reliable
method of assessment. This can be a problem in palliative care
where studies have found only a modest correlation between symptom
assessment by patients and symptom assessment by clinicians. The
same modest correlation in symptom assessment has been found between
patients and families. In addition, patients who are very weak
or ill may not be well enough to report symptoms or their reports
may be affected by cognitive impairment.
Two further
complexities exist when assessing symptoms:
- Symptoms
are often not dichotomized into present and absent. Symptoms
are present in a spectrum of severity from none to overwhelming;
- Assessment
methods involve issues such as who gives the information? Is
it assessed retrospectively or prospectively? what question
is asked? And do patients respond describing the treated symptom,
or its effect on them? For example, when bereaved family members
say that the patient had pain in the last year of life, are
they saying that the patient had pain, that was treated and
was controlled, or did they have pain that wasn't treated? Some
patients respond to the question "Do you have pain?"
with "Yes, I am taking a high dose of morphine for my pain."
|