Background: The Revised Illness Perception Questionnaire (IPQ-R) measures individuals' unique perceptions of their illness. While psychometric properties of the IPQ-R have been demonstrated in many disease populations, its content validity has not been extensively studied in non-dialysis chronic kidney disease (CKD). Unique features of CKD (e.g., few symptoms in early stages) may impact the measurement of illness perceptions. The purpose of this study was to explore the IPQ-R content validity in a sample of CKD patients.
Methods: Thirty-one participants completed the IPQ-R and were interviewed regarding their subscale scores (timeline, consequences, personal control, treatment control, coherence, cyclical, and emotions). Participants' agreement with their scores was tallied and assessed qualitatively for themes related to the content validity of the measure.
Results: Individual participant agreement with their subscale scores averaged 79% (range: 29-100%). Subscale agreement varied: timeline (100%), consequences, coherence, and emotion (83% each), cyclical (75%), personal control (65%), and treatment control (64%). A qualitative exploration of disagreement responses revealed concerns with the relevance and comprehensibility of personal control and treatment control.
Conclusions: Some IPQ-R subscales may pose content validity concerns in the non-dialysis CKD population. Item modification for comprehensibility (personal control) and relevance (treatment control) should be considered. Future studies should explore the impact of a patient's symptom experience on IPQ-R validity, especially in populations like CKD with a higher proportion of asymptomatic patients.
Keywords: chronic kidney disease; content validity; illness perception questionnaire; illness perceptions; illness representation; psychometric testing.