Facets of Measurement

A facet refers to an internally consistent and clinically relevant aspect of a particular clinical phenomena. A facet can represent a general construct (trait in the terminology of Campbell & Fiske). A facet can also represent a more specific aspect of a broader construct. For example, although a general facet could represent the construct of depression, the general facet of depression could be broken down into cognitive, emotional, motivational, behavioral, and somatic subfacets. Given that the level of specificity can be increased indefinitely, both theoretical and practical considerations (e.g., what judgments will be based on the obtained measures) are important in the determination of the level of specificity appropriate for the particular research and clinical goals.

A facet contains the population of elements relevant to the construct (or subconstruct), and these elements provide the basis for the selection of interview questions, rating scale items, self-monitoring items, behavioral codes, stimuli for laboratory measures, and so on. The elements within a facet should be highly correlated with each other. Each element within a facet should also correlate higher with its own facet (convergent validity) than with other facets (discriminant validity). This aspect of discriminant validity is all too seldom considered in the development of measures (Burns & Walsh, 2002). Content validity is critical here because it ensures that the facets and elements in the measure appropriately reflect the facets and elements of the construct (Haynes et al., 1995). Without good content validity, there is a strong likelihood that the outcomes from CFA and other procedures (e.g., item response theory analyses) will be difficult to interpret.

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