Item reduction based on rigorous methodological guidelines is necessary to maintain validity when shortening composite measurement scales

Objective: To review current practice and update guidelines for the methodology of shortening composite measurement scales (CMSs).

Study design and setting: A literature review gathered data on 91 shortening processes from 1995 to 2009. The validity of the initial CMS, the shortening methods, and the validity of the derived short-form scales were examined. The results were compared with those from a previous literature review (articles from 1985 to 1995) to develop updated guidelines for CMS shortening.

Results: The literature review revealed a persisting lack of use of rigorous methodology for CMS shortening. Of the 91 cases of CMS shortening, 36 combined a content approach and a statistical approach; 45 used only a statistical approach and 10 (11%) only a content approach. The updated guidelines deal with the validity and conceptual model of the initial CMS, the preservation of content and psychometric properties during shortening, the selection of items, and the validation of the short form.

Conclusion: Item reduction based on a rigorous methodology is necessary if the short-form instrument aims to maintain the validity and other measurement properties of the parent instrument, which in turn supports application in research and clinical practice.