Identifying the minimal important difference in patient-reported outcome measures in the field of people with severe mental illness: a pre–post-analysis of the Illness Management and Recovery Programme

PURPOSE: Complementary interventions for persons with severe mental illness (SMI) focus on both personal recovery and illness self-management. This paper aimed to identify the patient-reported outcome measures (PROMs) associated with the most relevant and meaningful change in persons with SMI who attended the Illness Management and Recovery Programme (IMR). METHODS: The effect of the IMR was measured with PROMs concerning recovery, illness self-management, burden of symptoms and quality of life (QoL). From the QoL measures, an anchor was chosen based on the most statistically significant correlations with the PROMs. Then, we estimated the minimal important difference (MID) for all PROMs using an anchor-based method supported by distribution-based methods. The PROM with the highest outcome for effect score divided by MID (the effect/MID index) was considered to be a measure of the most relevant and meaningful change. RESULTS: All PROMs showed significant pre–post-effects. The QoL measure ‘General Health Perception (Rand-GHP)’ was identified as the anchor. Based on the anchor method, the Mental Health Recovery Measure (MHRM) showed the highest effect/MID index, which was supported by the distribution-based methods. Because of the modifying gender covariate, we stratified the MID calculations. In most MIDs, the MHRM showed the highest effect/MID indexes. CONCLUSION: Taking into account the low sample size and the gender covariate, we conclude that the MHRM was capable of showing the most relevant and meaningful change as a result of the IMR in persons with SMI.