Item Parameter Drift of the Self-Description Questionnaire I

The purpose of this study was to evaluate the psychometric properties of the Self-Description Questionnaire I (SDQI) with regard to children’s mathematics self-concept based on the item response theory (IRT) framework. The researchers adopted the IRT-based techniques for uncovering item-level characteristics including discrimination ( a parameter) and thresholds ( b parameters). The data for this study were drawn from the Early Childhood Longitudinal Study, Kindergarten Class of 1998–99 (ECLS-K) with a sample of 14,631 children. The IRT-based evaluations suggest that the SDQI items have sufficient discrimination, but insufficient item thresholds in assessing third- and fifth-graders’ mathematics self-concept. Thus, it is recommended that the current SDQI be reconsidered for its age appropriateness. In addition, affective items, which involve enjoyment, liking, and positive emotions, are found to be better indicators of self-concept than cognitive items, which involve perceived competence, ability beliefs, and self-efficacy. Results also indicate the presence of item parameter drift (IPD) in all SDQI items, suggesting beta change of the scale over time – children become more sensitive to the response anchors as they grow older. Findings of this study provide insights into the conceptualization and operationalization of academic self-concept, as well as practical implications for future use and development of self-concept measures.

Psychometric Consequences of Subpopulation Item Parameter Drift

This study defines subpopulation item parameter drift (SIPD) as a change in item parameters over time that is dependent on subpopulations of examinees, and hypothesizes that the presence of SIPD in anchor items is associated with bias and/or lack of invariance in three psychometric outcomes. Results show that SIPD in anchor items is associated with a lack of invariance in dimensionality structure of an anchor test, a lack of invariance in scaling coefficients across subpopulations, and a lack of invariance in ability estimates. It is demonstrated that these effects go beyond what can be understood from item parameter drift or differential item functioning.