OBJECTIVES: Estimating the minimal important difference (MID) of patient reported outcome (PRO) measures is important to guide interpretations of scores and for assessing treatment efficacy in clinical trials and studies. The current study was designed to estimate the MID of newly developed PROs for Multiple Sclerosis (MS); The Patient Reported Indices for Multiple Sclerosis (PRIMUS; which includes Activity and Quality of Life (QoL) scales) and Unidimensional Fatigue Impact Scale (U-FIS). The measures have been shown previously to be unidimensional, valid and reliable.
METHODS: Data were taken from the TRANSFORMS study, a multi-country phase III study evaluating the safety and efficacy of oral fingolimod compared to IFNB-1a i.m. in relapsing-remitting MS patients. PRO assessments were completed at baseline, 6 and 12 months. Measures included the PRIMUS-Activities (scored 0–30), PRIMUSQoL (scored 0–22), U-FIS (scored 0–66) and EQ-5D. For PRIMUS and U-FIS scales, a high score indicates more severe impact. Both anchor (published EQ-5D MID values) and distribution (0.2 and 0.5 effect sizes, standard error of measurement) based approaches were employed. Anchor-based MID values were assessed both for individuals who improved or deteriorated according to EQ-5D MID values. Triangulation of results provided the final PRIMUS and U-FIS MID estimates.
RESULTS: Trial sample: n 1292, 67.3% female, mean age 36.2 (SD 8.5), mean MS duration 7.4 years (SD 6.2). Anchor and distribution based MID’s ranged from 0.9–2.9 (PRIMUS QoL), 0.7–2.3 (PRIMUS Activities) and 2.4–7.3 (U-FIS). Triangulation resulted in the following MID values; PRIMUS Activities 1.5 for individuals improving or deteriorating; PRIMUS QoL 1.5 for individuals improving or deteriorating and U-FIS 4.5 for those improving and 5.0 for those deteriorating.
CONCLUSIONS: The analyses provide preliminary information on the interpretation of scores on the scales. The MID values will aid the assessment of treatment efficacy in clinical trials and studies.
