Objective: The Revised Illness Perceptions Questionnaire (IPQ-R), widely used to assess illness perceptions, may fail to measure unique characteristics of different illnesses. This study modified and validated the IPQ-R for breast cancer survivors to provide detailed understanding of the specific illness perceptions held by these patients.
Design: Initial modifications were made following qualitative interviews and were revised in a think-aloud study. The modified scale was tested in 753 breast cancer survivors prescribed tamoxifen. Modifications included adding a tamoxifen consequences scale and adapting the timeline scales to measure beliefs around risk of recurrence and cure. A confirmatory factor analysis was conducted on the modified questionnaire and an exploratory factor analysis on the causal beliefs scale. Test-retest reliability, internal consistency and construct validity were also examined.
Results: The proposed eight-factor structure showed acceptable model fit, with high loadings and good reliability for all subscales. Correlations between subscales were consistent with theory and previous research.
Conclusions: The IPQ-BCS is valid and reliable, and provides unique understanding of specific perceptions held by this population, including beliefs surrounding risk of recurrence and consequences of ongoing hormonal treatment. Identifying these perceptions will aid development of interventions targeting depression, fear of recurrence and medication non-adherence.
Keywords: IPQ-R; breast cancer; confirmatory factor analysis; illness perceptions; scale validation; tamoxifen.