Psychometric properties of the Brief Illness Perception Questionnaire (Brief-IPQ) in periodontal diseases

Aim: To investigate the psychometric properties of the validated Portuguese version of the Brief Illness Perception Questionnaire (Brief-IPQ) in patients with gingivitis and periodontitis.

Material and methods: This study enrolled 571 patients with periodontal diseases (PDs) (67 gingivitis and 504 periodontitis cases), in a population-based epidemiologic survey conducted at the health centres in the South Lisbon Metropolitan Area. Brief-IPQ, a 9-item self-reported scale, reliability was evaluated using Cronbach's alpha. Confirmatory factor analysis (CFA) was used to construct validation. Multigroup analysis tested invariance across gender.

Results: The Brief-IPQ showed acceptable reliability (α = .80). Confirmatory factor analysis revealed good model fit (χ² (16) = 41.236, GFI = 0.982, CFI = 0.985, RMSEA = 0.053). All factors loaded similarly to the original Brief-IPQ scale, with the exception of the "personal control" domain. Periodontal patients downgrade its illness and likely impact. The "consequences" domain showed significant positive correlations with all factors, except "treatment control" and "understanding" domains. The "concern" and "emotional response" domains had the highest significant correlation. Multigroup analysis findings supported factor invariance across the sex groups.

Conclusion: The Brief-IPQ revealed acceptable reliability, construct factorial validity and invariance across gender. This short instrument may be used as an easily applicable and valuable tool to determine illness perception in patients with PDs.