Research Council breathlessness scale.20 Fifteen questions
were taken from the CAT and SGRQ questionnaires that
referred to individuals’ experiences with dyspnea, and a
composite measure of dyspnea impact using a weighted
sum of the responses to the 15 questions was constructed.
Questions were coded so that larger values indicate more
impactful dyspnea. Weights used for question responses
in calculating the dyspnea impact assessment measure
were those of theﬁrst component of a principal compo-
nent analysis (PCA) based on the covariance matrix of
question responses. Questions with multiple responses
and ordinal structure are individually more informative
and thus were accorded higher weight than individual
true-false questions. No additional PCA component was
anticipated a priori to be material for our investigation,
and an eigenvalue analysis of the PCA was conducted to
verify this assumption.
The composite dyspnea impact measure was scaled so its
minimum value was 0 if the response to each of the 15
questions was 0, and the maximum value was scaled to
100 if the individual responses for all 15 questions rep-
resented the most severe dyspnea response.
1298 Original Research [ 166#6 CHEST DECEMBER 2024 ]