Validity of the Brief Illness Perception Questionnaire in people with knee pain: a Rasch analysis
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Objective: The Brief Illness Perception Questionnaire (B-IPQ) is a frequently used measure of illness perception (IP). The aim of this study was to explore the psychometric properties of the questionnaire when used in elderly people with knee pain. Method: Based on data from the Frederiksberg Cohort on elderly people reporting knee pain (N = 836), the psychometric properties of the eight B-IPQ items (1 ‘Consequences’, 2 ‘Timeline’, 3 ‘Personal control’, 4 ‘Treatment control’, 5 ‘Identity’, 6 ‘Concern’, 7 ‘Coherence’, and 8 ‘Emotions’) were analysed using Rasch analysis to establish whether the questionnaire provides reliable and valid measures of IP. Results: Threshold disordering was found on the 1–10 rating scale in all items. When rescaling to a 0–2 rating scale, disordering was resolved in six items. Item goodness-of-fit analyses revealed that two items displayed underfit misfit and four items overfit misfit; hence, the B-IPQ does not present unidimensionality. The person separation index indicated that items separate respondents into only two IP levels. Finally, floor and ceiling effects were found, indicating that the B-IPQ may not fully describe the extent of IP in this population. Conclusion: The 1–10 rating scale used in the Danish B-IPQ targeting knee pain is suboptimal, while a 0–2 scale improves the psychometric properties of the scale. The B-IPQ does not present unidimensionality and the use of a sum score is therefore not recommended when assessing IP. The B-IPQ may not cover the extent of IP in elderly people with knee pain.
Original language | English |
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Book series | Scandinavian Journal of Rheumatology |
Volume | 53 |
Issue number | 1 |
Pages (from-to) | 63-71 |
Number of pages | 9 |
ISSN | 0300-9742 |
DOIs | |
Publication status | Published - 2023 |
Bibliographical note
Publisher Copyright:
© 2023 Scandinavian Journal of Rheumatology Foundation.
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