Mokken scales for testing both pre- and postintervention: an analysis of the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM) before and after counseling.

Abstract

Mokken scaling is increasingly being applied to assessing the extent to which clinical scales possess clinically useful properties, especially invariant item ordering (IIO). These scales are often used to track progress in symptoms over time to evaluate the success of an intervention. Such interventions are designed to affect psychopathological trait levels overall but may in some cases act disproportionately on some symptoms over others. As a result, there is no guarantee that the item orderings of a clinical scale will be preserved between the point at which individuals begin treatment and the point at which they can be considered recovered. In these situations, many of the potential benefits of IIO are undermined because an IIO identified at either time point will not be informative about changes in symptoms over time. In this study, we aimed to assess the extent to which the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM) retained the same item orderings in a sample of individuals when initially presenting for counseling treatment and when discharged. From the 34 items of the CORE-OM we found a subset of 10 items exhibiting monotonicity, invariant item ordering, and highly similar item orderings when measured at both time points.