Improving measurement in health education and health behavior research using item response modeling: comparison with the classical test theory approach.

This paper compares the approach and resultant outcomes of item response models (IRMs) and classical test theory (CTT). First, it reviews basic ideas of CTT, and compares them to the ideas about using IRMs introduced in an earlier paper. It then applies a comparison scheme based on the AERA/APA/NCME 'Standards for Educational and Psychological Tests' to compare the two approaches under three general headings: (i) choosing a model; (ii) evidence for reliability--incorporating reliability coefficients and measurement error--and (iii) evidence for validity--including evidence based on instrument content, response processes, internal structure, other variables and consequences. An example analysis of a self-efficacy (SE) scale for exercise is used to illustrate these comparisons. The investigation found that there were (i) aspects of the techniques and outcomes that were similar between the two approaches, (ii) aspects where the item response modeling approach contributes to instrument construction and evaluation beyond the classical approach and (iii) aspects of the analysis where the measurement models had little to do with the analysis or outcomes. There were no aspects where the classical approach contributed to instrument construction or evaluation beyond what could be done with the IRM approach. Finally, properties of the SE scale are summarized and recommendations made.