Investigating Invariant Item Ordering in Personality and Clinical Scales: Some Empirical Findings and a Discussion

In recent studies, different methods were proposed to investigate invariant item ordering (IIO), but practical IIO research is an unexploited field in questionnaire construction and evaluation. In the present study, the authors explored the usefulness of different IIO methods to analyze personality scales and clinical scales. From the authors' analyses, it was clear that for clinical scales consisting of items that cover a limited range of "symptoms," the IIO property is an unrealistic assumption. For scales that consist of items that cover a broader range of item severity, IIO research can provide useful information. However, removing an item because it violates the assumption of IIO may be problematic because it can affect the construct that is measured. Finally, the authors advise researchers to always use plots of item rest-score regressions to interpret IIO results.