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Most surveys identify
cases of fatigue by using the descriptor "fatigue" or some
other simple descriptor (e.g. "lack of energy" or "weakness").
As discussed previously, the descriptors used to define eligibility
can have substantial impact on case ascertainment.
Question
9.1
Consider the following
eligibility criteria used in different surveys of fatigue
in populations undergoing therapy with a new biological response
modifier:
Protocol
#1: Inclusion criteria: ….Patients will be approached in the
infusion suite following their second cycle of therapy. To
determine eligibility for the survey, the patient will be
asked: "Have you experienced fatigue during the past week?"
Patients answering affirmatively will be asked to participate
in the survey.
Protocol #2: Inclusion
criteria: ….Patients will be approached in the infusion suite
following their second cycle of therapy. To determine eligibility
for the survey, the patient will be asked: "Have you experienced
fatigue severe enough to impair your ability to function during
the past week?" Patients answering affirmatively will be asked
to participate in the survey.
Protocol #3: Inclusion criteria: ….Patients will be approached
in the infusion suite following their second cycle of therapy.
To determine eligibility for the survey, the patient will
be asked to complete the following item: "How would you rate
your fatigue, on average during the past week, using a zero
to 10 scale, where 0 is no fatigue at all and 10 is the worst
fatigue that you can imagine?" Patients indicating a score
of 5 or greater will be asked to participate in the survey.
What do you conclude about case definition from this example?
 | Using
the word "fatigue" or "weakness," without additional qualifiers,
is best because the largest number of cases will be identified.
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 | Using
a precise numeric scale to define cases is best because
it increases the likelihood of identifying "real" cases
of pathologic fatigue, which would be of clinical interest.
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 | The
eligibility criterion for case definition should be fashioned
based on the goals of the study. There is no one best
approach. |
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