Jin-Shei Lai1, Rita Bode2, Hwee-Lin Wee3, David Eton4, David Cella11Department of Medical Social Sciences, 2Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, IL USA; 3Department of Pharmacy, National University of Singapore, Singapore; 4Division of Health Care Policy and Research, Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USAAbstract: We aimed to validate a more rapid, yet reliable means of assessing physical function (PF) for patients with prostate cancer. The sample included 128 prostate cancer patients recruited from urology and general oncology clinics at two Chicago-area hospitals. The main outcome measures were: A 36-item PF item bank that included a 5-item short form (BriefPF) and the 10-item PF subscale (PF-10) from the Medical Outcomes Study SF-36. Validity, information function, and relative precision (calculated using Rasch analysis and raw scores) of the BriefPF were compared to the PF-10 and the full PF item bank. We found that the BriefPF and PF-10 were strongly correlated (r = 0.85) with the PF bank, and all three scales differentiated patients according to performance status (FPF bank(2,124) = 32.51 P < 0.001, FPF-10(2,121) = 27.35 P < 0.001, FBriefPF (2,123) = 38.40 P < 0.001). BriefPF has excellent precision relative to the PF-10 in measuring patients with different performance status levels. The Rasch-based information function indicated that the BriefPF was more informative than PF-10 in measuring moderate to higher functioning patients. Hence, the BriefPF offers a parsimonious and precise measure of PF for use among men with prostate cancer, and may aid in the timely inclusion of patient-reported outcomes in treatment decision-making.Keywords: quality-of-life, item bank, short-form, Medical Outcomes Study