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Structural validity in the measurement of Holland's vocational typology : a measure of Holland's types scaled to an explicit circumplex model Trapnell, Paul David


A simple principal components procedure for constructing a multi-scale test to fit a circumplex structural model was illustrated. Loevinger's concept of structural validity, which specifies that test structure should faithfully reflect postulated structure within a domain, provided a psychometric rationale for applying circumplex scale construction procedures to the domain of vocational interests: although Holland's influential theory of career choice specifies an explicit two-dimensional circumplex model to describe the relations among the primary categories of vocational interest, and despite the extensive degree of validity established for the model, no measures of those interest variables have apparently been constructed explicitly to fit a two-dimensional circumplex model. In doing so, this study also tested the hypothesis that the two dimensions accounting for the well-known hexagonal arrangement of Holland's six vocational categories are continuous and that, within the two dimensional interest space, Holland's six categories represent but six points along what is a circular continuum. This hypothesis was tested by attempting to construct evenly spaced "octant" scales to mark the two-dimensional vocational interest space defined by Holland's six Vocational Preference Inventory (VPI) scales. Circumplex analysis procedures were applied to a large pool of occupational titles which included a large subset of VPI items. Items with the best circumplex properties in this pool were assembled into a set of scales to mark ideal octant locations around the two interest dimensions. Results provided strong support for a circumplex view of the dimensions accounting for Holland's hexagon, and evidence, in a validation sample, of a remarkably good fit of the new eight scales to an ideal circumplex structure. Implications of the presents results for Holland's theory and for circumplex approaches to measurement are discussed, as well as suggested applications of this efficient 64-item circumplex measure of Holland's "big two" dimensions of interests.

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