Is less more? A preliminary investigation of the number of response categories in self-reported pain

Karon F Cook¹, David Cella², Erin L Boespflug¹, Dagmar Amtmann¹

¹Department of Rehabilitation Medicine, University of Washington, Seattle, WA; ²Department of Medical Social Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA

Abstract: The purpose of this study was to conduct a preliminary investigation of the number of response options for self-reports of pain interference. Responses to interference items of the 11-category Brief Pain Inventory (BPI) were obtained in a sample of 434 persons from two sites and modeled using the partial credit model. In successive calibrations, response categories were collapsed and new scores were generated. Scores based on two to three categories produced poor results. Four to five categories yielded better results. However, scoring using more than five categories did not appreciably improve the reliability, person separation, or validity of scores. These results suggest that fewer response categories—as few as five or six–may function as well as the 11 response categories that are conventionally used. The results are preliminary since the number of response categories actually presented was not manipulated in the study design. Future research should compare the reliability and validity of scores based on the BPI interference items when items are presented with the conventionally 11-response format, versus presentation with fewer response options.

Keywords: psychometrics, outcomes, quality of life, measurement, pain