Detection and Validation of Unscalable Item Score Patterns using Item Response Theory : An Illustration with Harter's Self Perception Profile for Children

I illustrate the usefulness of person-fit methodology proposed in the context of item response theory in the field of personality assessment. First, I give a nontechnical introduction to existing person-fit statistics. Second, I analyze data from Harter's Self-perception Profile for Children (SPPC; Harter, 1985) in a sample consisting of children 8-12 years of age (N = 611) and argue that for some children the scale scores should be interpreted with care. Combined information from person-fit indices and from observation, interviews, and self-concept theory showed that similar score profiles have a different interpretation. For some children in the sample due to a less developed self-concept and/or problems understanding the wording of the questions, item scores did not adequately reflect their trait level. I recommend investigating the scalability of score patterns when using self-report inventories to withhold the researcher from wrong interpretations.