Comparison of Distribution‐ and Anchor‐Based Approaches to Infer Changes in Health‐Related Quality of Life of Prostate Cancer Survivors

Abstract

Objective. To determine the minimal important difference (MID) in generic and prostate-specific health-related quality of life (HRQoL) using distribution-and anchorbased methods. Study Design and Setting. Prospective cohort study of 602 newly diagnosed prostate cancer patients recruited from an urban academic hospital and a Veterans Administration hospital. Participants completed generic (SF-36) and prostate-specific HRQoL surveys at baseline and at 3, 6, 12, and 24 months posttreatment. Anchor-based and distribution-based methods were used to develop MID estimates. We compared the proportion of participants returning to baseline based on MID estimates from the two methods. Results. MID estimates derived from combining distribution-and anchor-based methods for the SF-36 subscales are physical function = 7, role physical = 14, role emotional = 12, vitality = 9, mental health = 6, social function = 9, bodily pain = 9, and general health = 8; and for the prostate-specific scales are urinary function = 8, bowel function = 7, sexual function = 8, urinary bother = 9, bowel bother = 8, and sexual bother = 11. Proportions of participants returning to baseline values corresponding to MID estimates from the two methods were comparable. Conclusions. This is the first study to assess the MID for generic and prostate-specific HRQoL using anchor-based and distribution-based methods. Although variation exists in the MID estimates derived from these two methods, the recovery patterns corresponding to these estimates were comparable. Key Words. Prostate cancer, health-related quality of life, minimal important difference, anchor based, distribution basedIn the era of comparative effectiveness, health status measures are assuming importance in the arena of patient-reported outcomes. Health-related quality of life (HRQoL) is an important component of patient-reported outcomes

Minimally Important Difference for the Expanded Prostate Cancer Index Composite Short Form

“…Comparisons to other quality of life instruments have revealed cutoffs for symptom severity in different domains, 18,19 although there have never been thresholds for symptom improvement or worsening developed for the EPIC-26 instrument. Our findings, along with recent work in this area using the UCLA-Prostate Cancer Index (UCLA-PCI) 20 and EPIC-CP, 16 builds a strong foundation for understanding meaningful differences in patient-reported outcomes among survivors. For example, comparable MID values for the UCLA Prostate Cancer Index, 20 a precursor of EPIC also scored from 0–100, were found for urinary function (8) and bother (9), bowel function (7) and bother (8), and sexual function (8) and bother (11).…”

“…Our findings, along with recent work in this area using the UCLA-Prostate Cancer Index (UCLA-PCI) 20 and EPIC-CP, 16 builds a strong foundation for understanding meaningful differences in patient-reported outcomes among survivors. For example, comparable MID values for the UCLA Prostate Cancer Index, 20 a precursor of EPIC also scored from 0–100, were found for urinary function (8) and bother (9), bowel function (7) and bother (8), and sexual function (8) and bother (11). That the upper bounds of thresholds in our study closely match these values supports construct validity and robustness of the recommended MID levels.…”

Caution with Use of the EPIC-50 Urinary Bother Scale: How Voiding Dysfunction Modifies its Performance

“…Levels of agreement (or disagreement) between function and bother were defined in relation to previously published minimally important differences (MIDs) in PCa survivors: 5-9 in the urinary domain and 10-12 in the sexual domain. 16, 17 Although these values were derived from the University of California, Los Angeles – Prostate Cancer Index and the EPIC-26 rather than the EPIC-50, the high correlation between the EPIC-26 and -50 (0.96-1.00) 18 suggests these MIDs likely also apply to the EPIC-50. 16 In our analysis, we used the upper bounds of the MID ranges, 9 in the urinary domain and 12 in the sexual domain, to provide conservative estimates of disagreement between function and bother.…”

Stereotactic Body Radiation Therapy for Prostate Cancer: What Is the Appropriate Patient-Reported Outcome for Clinical Trial Design?

“…An MID is the smallest difference in a questionnaire domain score, which patients perceive as a meaningful change (26). The MID for a given domain is important in determining the required number of patients for study recruitment and interpreting the questionnaire results.…”

“…The most commonly used statistical approach is to utilize one-half SD of the baseline domain score (23), which is specific to the patient population being analyzed. Such a distribution approach has been criticized because it does not provide information on the clinical relevance of the observed change (26). In general, most approaches lead to MIDs that are 5-10% of the instrument range (23)(24)(25)28).…”