What do people think about when they answer the Brief Illness Perception Questionnaire? A 'think-aloud' study

Objectives. The Brief Illness Perception Questionnaire (Brief IPQ) is a commonly used questionnaire that aims to assess patients' illness beliefs. There is, however, no direct information on how people interpret and respond to this questionnaire, nor on the nature and extent of problems people have when completing it. The present study describes the problems that patients encounter when completing the Brief IPQ. Design. Cross-sectional observational study. Methods. A 'think-aloud' method was employed with two samples: 6 patients attending a preoperative exercise programme in secondary care, and 11 patients receiving physiotherapy in primary care. Results. In total, 88 problems were identified, mostly (N = 45) consisted of participants rereading a question or stumbling in reading it. In 8 cases, participants misinterpreted a question. The pattern of findings was striking similar across the two samples. The questions about identity, personal control, illness coherence, and causal attributions yielded most difficulties (18, 16, 16, and 11 problems, respectively). Conclusions. Given that the Brief IPQ assesses each construct with a single item, the number of problems people have with completing it is particularly problematic, and calls into question the content validity of this measure. Further developmental work with this questionnaire may be needed to better quantify and resolve the problems identified.