Scale structure
The scale structure refers to the set formed by the different items of
the questionnaire, representing a certain construction (if they evaluate
QoL or severity), and can be tested, for example, by factor analysis.
Factor analysis is most commonly used to test the uni-dimensionality of
the construct and is based on correlations of the items. If the
correlation factor for a particular item is <0.40, those items
can be removed from the questionnaire, as they do not show to belong to
the set of questions in the remaining items 5,7.
Factor analysis can be comprised into: exploratory factor analysis and
confirmatory factor analysis. At times, a Pearson’s correlation
coefficients in order to explore all interactions of items pairs and to
be excluded before conducting factor analyses 8.