Using Item Response Theory (IRT) for Developing and Evaluating the Pain Impact Questionnaire (PIQ‐6™)

Objectives.  To describe the development and evaluation of the Pain Impact Questionnaire (PIQ‐6 TM ), a six‐item measure of pain severity and impact on health‐related quality of life (HRQOL) domains. Participants.  Two general US population samples (N = 829 and N = 7,025) and one chronic pain patient sample (N = 350) were included. Methods.  The PIQ‐6 TM was developed using conventional and item response theory (IRT) methods in four steps: 1) initial selection and development of items based on results from a previously developed Bodily Pain item bank; 2) final item selection based on new data and investigations of unidimensionality, differential item functioning (DIF), and IRT modeling; 3) development of scoring algorithms, population norms, and cross‐calibrations; and 4) psychometric evaluation. Results.  Six items on pain intensity and impact satisfied requirements of unidimensionality and lack of DIF and could be scored using IRT methods. The PIQ‐6 showed good internal consistency reliability (coefficient alpha = 0.94) and good construct validity. Convergent validity was supported by strong correlations with pain severity scales ( visual analog and numerical rating scales; r  = 0.81–0.84); discriminant validity was suggested by correlations with the SF‐8™ Health Survey Physical and Mental Component Summary measures ( r  = −0.77; r  = −0.32, respectively), significant mean score differences between chronic pain patients and the general population, and between patients differing in self‐reported medical conditions ( P  < 0.001). Conclusion.  The PIQ‐6 is a brief, precise questionnaire available in a paper‐and‐pencil version and a computerized version that includes scoring and feedback software. It may facilitate large‐scale, inexpensive, precise, and norm‐based pain assessment and monitoring in a wide variety of settings (e.g., homes, clinics, offices).