Thurstonian item response theory and an application to attitude items

Abstract

The assessment of attitudes has a long history dating back at least to the work of Thurstone. The Thurstonian approach had its “golden days,” but today it is seldom used, partly because judges are needed to assess the location of an item, but also because of the emergence of contemporary tools such as the IRT. The current work is motivated by a study that assesses medical students’ attitudes toward obese patients. During the item-development phase, the study team discovered that there were items on which the team members could not agree with regard to whether they represented positive or negative attitudes. Subsequently, a panel of n=201 judges from the medical profession were recruited to rate the items, and the responses to the items were collected from a sample of n=103 medical students. In the current work, a new methodology is proposed to extend the IRT for scoring student responses, and an affine transformation maps the judges’ scale onto the IRT scale. The model also takes into account measurement errors in the judges’ ratings. It is demonstrated that the linear logistic test model can be used to implement the proposed Thurstonian IRT approach.