Dagmar Amtmann, Jiseon Kim, Hyewon Chung, Robert L Askew, Ryoungsun Park, Karon F Cook

The minimally important difference (MID) refers to the smallest change that is sufficiently meaningful to carry implications for patients' care. MIDs are necessary to guide the interpretation of scores. This study estimated MID for the Patient Reported Outcomes Measurement Information System (PROMIS) pain interference (PI). Study instruments were administered to 414 people who participated in two studies that included treatment with low back pain (LBP; n=218) or depression (n=196). Participants with LBP received epidural steroid injections and participants with depression received antidepressants, psychotherapy, or both. MIDs were estimated for the changes in LBP. MIDs were included only if a priori criteria were met (ie, sample size ≥10, Spearman correlation ≥0.3 between anchor measures and PROMIS-PI scores, and effect size range =0.2-0.8). The interquartile range (IQR) of MID estimates was calculated. The IQR ranged from 3.5 to 5.5 points. The lower bound estimate of the IQR (3.5) was greater than mean of standard error of measurement (SEM) both at time 1 (SEM =2.3) and at time 2 (SEM =2.5), indicating that the estimate of MID exceeded measurement error. Based on our results, researchers and clinicians using PROMIS-PI can assume that change of 3.5 to 5.5 points in comparisons of mean PROMIS-PI scores of people with LBP can be considered meaningful.