Minimally important differences were estimated for six Patient-Reported Outcomes Measurement Information System-Cancer scales in advanced-stage cancer patients

Objective: We combined anchor- and distribution-based methods to establish minimally important differences (MIDs) for six Patient-Reported Outcomes Measurement Information System (PROMIS)-Cancer scales in advanced-stage cancer patients. Study Design and Setting: Participants completed 6 PROMIS-Cancer scales and 23 anchor measures at an initial (n = 101) assessment and a follow-up (n = 88) assessment 6-12 weeks later. Three a priori criteria were used to identify usable cross-sectional and longitudinal anchor-based MID estimates. The mean standard error of measurement was also computed for each scale. The focus of the analysis was on item response theory-based MIDs estimated on a T-score scale. Raw score MIDs were estimated for comparison purposes. Results: Many cross-sectional (64%) and longitudinal (73%) T-score anchor-based MID estimates were excluded because they did not meet a priori criteria. The following are the recommended T-score MID ranges: 17-item Fatigue (2.5-4.5), 7-item Fatigue (3.0-5.0), 10-item Pain Interference (4.0-6.0), 10-item Physical Functioning (4.0-6.0), 9-item Emotional Distress-Anxiety (3.0-4.5), and 10-item Emotional Distress-Depression (3.0-4.5). Effect sizes corresponding to these MIDs averaged between 0.40 and 0.63. Conclusions: This study is the first to address MIDs for PROMIS measures. Studies are currently being conducted to confirm these MIDs in other patient populations and to determine whether these MIDs vary by patients' level of functioning.