Traitedness and the Assessment of Response Pattern Scalability

Scalability statistics are used to measure the degree to which an examinee's item responses to a self-report measure conform to a specified pattern. This article proposes that a scalability index based on item response theory, called Z_L, offers promise for detecting individual differences in traitedness. The Z_L index is described and applied to data from 1,000 Ss who were administered the Multidimensional Personality Questionnaire (A. Tellegen, 1982). Low split-half reliabilities were found for Z_L index scores computed within 11 personality scales. However, further data scrutiny revealed that valuable information about an individual's trait structure can still be gleaned from a scalability analysis. It is concluded that scalability indices can be used, albeit judiciously, to explore the fit between an individual's behavior and a personality trait construct.