One, two, or three? Constructs of the brief pain inventory among patients with non-cancer pain in the outpatient setting

Abstract

CONTEXT: Either a two-factor representation (pain intensity and interference) or a three-factor representation (pain intensity, activity interference, and affective interference) of the modified Brief Pain Inventory (BPI) is appropriate among cancer patients. OBJECTIVES: To evaluate the extent to which a three-factor representation (pain intensity, activity interference, and affective interference) is appropriate for BPI among patients with noncancer pain seen in an outpatient setting. METHODS: We conducted a prospective, multicenter, observational, nonrandomized study using patient pain registry data from outpatient settings. Seven hundred forty-one patients with acute episodes of noncancer pain requiring treatment with a prescription medication containing oxycodone immediate-release on an as-needed basis for at least five days participated. Baseline measurements included the modified BPI pain intensity (right now, average, and worst in 24 hours) and pain interference with general activities, walking, work, mood, relations with others, sleep, and life enjoyment. Confirmatory factor analysis was conducted for the overall sample and among postoperative patients (n = 133), patients with back and neck pain (n = 202), patients with arthritis (n = 148), and patients with injury or trauma (n = 204). RESULTS: Both the two-factor and three-factor models were statistically better than the one-factor model (P < 0.05), with the two-factor model performing better than the three-factor model. Configural invariance, but not metric invariance by patient cohort group was demonstrated. CONCLUSION: Consistent with analyses among cancer patients, a two-factor representation of BPI is appropriate for noncancer patients seen in an ambulatory setting. This work lends additional support for the psychometric properties of BPI. All rights reserved.