A Comparison of Adjacent Categories and Cumulative Differential Step Functioning Effect Estimators

The study of measurement invariance in polytomous items that targets individual score levels is known as differential step functioning (DSF). The analysis of DSF requires the creation of a set of dichotomizations of the item response variable. There are two primary approaches for creating the set of dichotomizations to conduct a DSF analysis: the adjacent categories approach, and the cumulative approach. To date, there is limited research on how these two approaches compare within the context of DSF, particularly as applied to a real data set. This study evaluated the results of a DSF analysis using both dichotomization schemes in order to determine if the two approaches yield similar results. The results revealed that the two approaches generally led to consistent results, particularly in the case where DSF effects were negligible. However, when significant DSF effects were present, the two approaches occasionally led to differing conclusions.