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Many
people experience fleeting pain in various body locations from
time to time. A question that simply asks whether a person has
experienced pain in the muscles of the face or the joint in front
of the ear is likely to yield a number of "cases" whose
pain is not very severe or long lasting. Thus, researchers who
are interested in quantifying the burden of TMD in the population
may wish to eliminate these short-lived, mild cases.
In one study
(Von
Korff et al., 1988) subjects were specifically asked not to
report pain experiences that were fleeting or minor, and to report
only pain that lasted a whole day or more or occurred several
times in a year, i.e., a threshold based on either episode duration
or episode frequency.
Other studies
set a threshold using pain frequency as the only criterion. For
example, Goulet
et al. (1995) asked about TMD pain that occurred "often
or very often," and List
et al. (1999) considered as possible cases only those subjects
who reported pain occurring once a week or more.
Such thresholds
for severity and persistence can markedly change prevalence rates.
As a practical matter, to keep questions from becoming too complicated,
questions that inquire into the presence of pain are generally
asked as "filter" questions, and then those who report
pain are asked to rate the severity or persistence of the pain.
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