The Interpersonal Mindfulness Scale (IMS) was recently developed to assess the qualities of mindfulness relevant to interpersonal interactions. The objective of the current study was to create a valid and reliable short-form version from the existing 27-item IMS.
Rasch modeling methods were used to evaluate a 17-item version and 13-item version of the IMS-short form (IMS-SF) in a sample of 584 participants (sample A). Items from the IMS were deleted with the goals to maintain the theoretical representation of the construct and to retain at least three items from each subscale. An independent sample of 503 participants (sample B) was used to examine the robustness of each IMS-SF.
In both samples, the 17-item and 13-item versions of the IMS-SF met the expectations of the unidimensional Rasch model, were invariant across demographic factors, and had acceptable reliability (PSI = 0.74–0.81). The 17-item version demonstrated better reliability and coverage of the construct in both samples compared to the 13-item version. Nevertheless, the 13-item IMS-SF maintained satisfactory psychometric properties to be recommended as a briefer alternative for most research uses. Zero-order correlations and partial correlations, controlling for trait mindfulness, supported the construct validity of each IMS-SF. The accuracy of measurement of the IMS-SF can be enhanced by transforming ordinal responses into interval-level data using the included ordinal-to-interval conversion tables.
Both the 17-item and 13-item IMS-SF can be used to efficiently measure overall levels of interpersonal mindfulness.