Estimates for Minimally Important Differences (MIDs) for two patient-reported outcome measurement information system computer-adaptive-tests in chronic pain outpatients

      We combined anchor- and distribution-based methods to evaluate responsiveness and establish minimally important differences (MIDs) for 2 Patient-Reported Outcomes Measurement Information System (PROMIS) measures in a chronic pain population. These included the computer-adaptive-test (CAT) versions of 2 PROMIS measures: Depressive Symptoms and Anxiety-Related Symptoms (PROMIS; Cella et al., 2007). Depressive and anxiety-related symptoms are the most common psychological symptoms experienced by individuals with chronic/persistent pain (Gatchel, 2004). By identifying a usable MID range, reliable references of treatment response will be established for these four PROMIS measures for this population. Study Participants undergoing a Behavioral Medicine Evaluation in an Interdisciplinary Pain Management clinic completed 4 PROMIS computer-adaptive-tests and multiple clinical anchor measures/questions. Modeled after similar analyses (Yost et al., 2011), three a priori criteria were used to select usable cross-sectional anchor-based MID estimates; these included a minimum Spearman correlation of 0.3 between the PROMIS measure and anchor item/categories, minimum comparison group sample size of 10 within each anchor, and an effect size between 0.2 – 0.8 for each anchor-based estimate. For each PROMIS measure, the mean standard error of measurement was calculated and incorporated into MID analyses. A number of the cross-sectional T-score anchor-based MID estimates (61%) were not included due to failure to meet a priori criteria. Based on analyses, the following T-score MID ranges are recommended: Depression CAT (3.0 – 5.5) and Anxiety CAT (3.0 – 5.0). The average effect sizes for MID estimates ranged from 0.31 – 0.75. This study is among the first to address MIDs for PROMIS measures; it represents the first study to establish usable MIDs for psychological symptoms with outpatients with chronic/persistent pain. Results may be used to gauge minimally important clinical differences and/or treatment response for individuals within this patient population.