Interpreting the Clinical Significance of Quality of Life Score Changes after Radiotherapy for Localized Prostate CancerPinkawa M. · Holy R. · Piroth M.D. · Klotz J. · Pfister D. · Heidenreich A. · Eble M.J.
a Department of Radiation Oncology; b Department of Urology, RWTH Aachen University, Aachen, Germany
Background: The assessment of a clinical significance of certain quality of life score changes is often controversially discussed. Materials and Methods: The Expanded Prostate Cancer Index Composite questionnaire was completed before and 3 times after treatment for prostate cancer by 756 patients. Two criteria were considered as a clinically relevant change: score change corresponding to at least ‘very small problem’ from the patient’s point of view; score change with significantly increasing incidence of symptoms. These changes were compared to the 50% of standard deviation (SD) threshold. Results: Patients assess mean changes up to 4 points to be ‘no problem’, suggesting a mean change of 5 points to be the minimal important difference. With increasing score changes significant changes were noticed in an increasing number of items: up to 4 items if scores decreased 5–10 points. Additionally, an increasing percentage of patients were affected. These results correlated well with the 50% of SD threshold. Conclusions: The threshold of 5 points (or 5% of the instrument range) can be interpreted as the minimal important difference of clinical significance. The proposed criteria corresponded well to the distributionbased criterion based on the 50% of SD level.
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