Original Research

Abstract

The Brief Pain Inventory–Short Form (BPI-SF) is widely used for assessing pain in clinical and research studies. The worst pain rating is often the primary outcome of interest; yet, no published data are available on its minimally important difference (MID). Breast cancer patients with bone metastases enrolled in a randomized, double-blind, phase III study comparing denosumab with zoledronic acid for preventing skeletal related events and completed the BPI-SF, FACT-B, and EQ-5D at baseline, week 5, and monthly through the end of the study. Anchor- and distribution-based MID estimates were computed. Data from 1,564 patients were available. Spearman correlation coefficients for anchors ranged from 0.33–0.65. Mean change scores for worst pain ratings corresponding to one-category improvement in each anchor were 0.26–1.04 for BPI-SF current pain, −1.40 to −2.42 for EQ-5D Index score, 1.71–1.98 for EQ-5D Pain item, −2.22 to −0.51 for FACT-B TOI, −1.61 to −0.16 for FACT-G Physical, and −1.31 to −0.12 for FACT-G total. Distribution-based results were 1 SEM = 1.6, 0.5 effect size = 1.4, and Guyatt's statistic = 1.4. Combining anchor- and distribution-based results yielded a two-point MID estimate. An MID estimate of two points is useful for interpreting how much change in worst pain is considered clinically meaningful.