Item response theory in affective instrument development: an illustration.

The benefits of item response theory (IRT) analysis in obtaining empirical support for construct validity make it an essential step in the instrument development process. IRT analysis can result in finer construct interpretations that lead to more thorough descriptions of low- and high-scoring respondents. A critical function of IRT is its ability to determine the adequacy with which the attitude continuum underlying each dimension is assessed by the respective items in an instrument. Many nurse researchers, however, are not reaping the benefits of IRT in the development of affective instruments. The purpose of this article is to familiarize nurse researchers with this valuable approach through a description of the Facets computer program. Facets uses a one parameter (i.e., item difficulty) Rasch measurement model. Data from a survey of 525 new mothers that assessed the psychometric properties of the Postpartum Depression Screening Scale are used to illustrate the Facets program. It is hoped that IRT will gain increased prominence in affective instrument development as more nurse researchers become aware of computer programs such as Facets to assist in analysis.