Purpose: To examine the relationship between changes in health-related quality-of-life (HRQOL) on the EORTC Quality of Life Questionnaire (QLQ-C30), and patients' perceptions of HRQOL changes as measured by the Subjective Significance Questionnaire (SSQ).
Patients and methods: A total of 101 patients completed the QLQ-C30 on weeks 1, 4 and 7 of radical external-beam radiation therapy (RT) for localized cancer of the prostate. Patients rated their change in physical functioning, emotional functioning, social functioning, and overall/global quality of life (QOL) by completing a seven-category SSQ at weeks 4 and 7. The association between changes in the QLQ-C30 change and the corresponding SSQ ratings were determined by calculation of mean change scores for each SSQ category and by Spearman rank correlation coefficient analysis.
Results: Patients' completion of the QLQ-C30 and SSQ exceeded 95%. Statistically significant changes in fatigue, pain, appetite, diarrhea, and global QOL scores were detected during RT. For patients reporting 'a little' change in global QOL on the SSQ, absolute mean QLQ-C30 change scores ranged between 0 to 15 points with 12/16 mean change scores between 2.5 and 8.5 points. In the entire study sample, correlations between SSQ patient ratings and QLQ-C30 change scores were lower than previously reported, ranging between 0.15 and 0.24 for the four different domains, but were higher when QOL scores producing ceiling effects were omitted.
Conclusion: The SSQ and QLQ-C30 may measure related concepts that could assist in the interpretation of changes in scores and in the calibration of the QLQ-C30. However, the nature of this relationship could not be elucidated in this data set because of a lack of variance in HRQOL scores in the study sample. Further investigation should be carried out in study samples with sufficient variance to allow more robust conclusions.