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Sources of Funding: This work was supported by David H. Koch provided through the Prostate Cancer Foundation; the Sidney Kimmel Center for Prostate and Urologic Cancers; SPORE grant from the National Cancer Institute to Dr. H. Scher (grant number P50-CA92629); a National Institutes of Health/National Cancer Institute Cancer Center Support Grant to MSKCC (grant number P30-CA008748); a Movember grant to Dr. Vickers; and the Department of Defense Prostate Cancer Research Program (grant number W81XWH-13-2-0074).

Introduction

For purposes of both research and clinical quality assurance, doctors must be able to report and compare their results. In prostate cancer, comparing critical patient-reported outcomes such as urinary and erectile function is complicated by the use of different questionnaires, with some centers using EPIC, others using PCI and others using separate instruments for urinary and erectile score (e.g. SHIM and IPSS). We aimed to develop a method to convert scores between these four commonly used instruments.

Methods

Patient-reported data on urinary and sexual function were collected from 1,284 men with localized prostate cancer using the Expanded Prostate Index Composite (EPIC-26), UCLA Prostate Cancer Index (PCI), Sexual Health Inventory for Men (SHIM) and International Prostate Symptom Scale (IPSS) questionnaires. We investigated several methods to convert scores between questionnaires.

Results

Conversion between EPIC and PCI urinary and sexual function subscales is best achieved using only the subset of questions that were asked on both questionnaires. This means that sexual function focuses on erectile function and does not include libido, which is include only on the PCI. For the conversion between EPIC or PCI erectile function scores and the SHIM scores, we defined equivalent thresholds of poor, intermediate or good function respectively: EPIC/PCI 0 - 40 and SHIM 1-7; EPIC/PCI 41 - 59 and SHIM 8-16; EPIC/PCI 60 - 100 and SHIM 17-25. Urinary continence scores are highly correlated between PCI and EPIC (r=0.94). Multiple attempts were made to compare IPSS with EPIC and PCI, but after investigation, no comparison was possible due to differences in domains addressed by these questionnaires. Therefore, we do not believe a conversion between IPSS and either PCI or EPIC is appropriate.

Conclusions

We have introduced methods for converting scores between the EPIC, PCI and SHIM questionnaires. While these conversion methods may introduce a minor amount of imprecision, such imprecision is dwarfed by other factors (such as case mix and statistical imprecision). Our methods represent the best available tools for combining and comparing patient-reported outcomes assessed using different instruments.

Funding

This work was supported by David H. Koch provided through the Prostate Cancer Foundation; the Sidney Kimmel Center for Prostate and Urologic Cancers; SPORE grant from the National Cancer Institute to Dr. H. Scher (grant number P50-CA92629); a National Institutes of Health/National Cancer Institute Cancer Center Support Grant to MSKCC (grant number P30-CA008748); a Movember grant to Dr. Vickers; and the Department of Defense Prostate Cancer Research Program (grant number W81XWH-13-2-0074).