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The large
and variable nature of the conditions in which dyspnea is a complaint,
the variety of discrete sensations available against which to
evaluate dyspnea, and differences in the way individuals describe
their symptoms have significant implications for inferring the
health status of patients. For example, suppose patients used
"uncomfortable" and "in pain" interchangeably
to describe their symptoms on separate occasions because they
perceive no difference (i.e. no "distance") between
the terms. If health-care providers, on the other hand, pictured
a much larger conceptual distance between the two terms, they
might incorrectly infer their patients' health status.
Scaling
is all about quantifying the mysterious mental world of subjective
experience. (For more information about item analysis and scale
construction visit http://faculty.ncwc.edu/toconnor/308/308lect05.htm).
A scale is a set of items or questions designed to provide a measure
or estimate of feelings, attitudes, or symptoms. Frequently, when
an individual responds to a set of items, we generate a single
value or score to represent the overall amount or degree of a
person's experience or understanding. But dyspnea is a multidimensional
construct (i.e. a subjective experience of breathing discomfort
that consists of qualitatively distinct sensations that vary in
intensity) and dyspnea assessment requires methods designed to
help uncover multiple parameters or dimensions of sensory experience
(Harver and Maher, 1990).
Unidimensional scales work well when the concept (such as weight
or temperature) is unidimensional. But if the concept is multidimensional
a single value or score may not describe it well.
Both
clustering and multidimensional scaling methods are designed to
uncover possible parameters or dimensions of experience by asking
patients to select from lists of phrases or descriptors those
that describe their "uncomfortable awareness of breathing."
These scaling approaches do not depend on preconceived notions
of patient experiences and are not limited to the study of single
sensory aspects of breathing (Baird
and Noma, 1978).
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