Developing the LIFE Monitor to Assess Fidelity of MULTI+ for Inpatients with Mental Illness

Abstract The extent to which an intervention is implemented as intended (i.e., fidelity) is rarely measured in complex lifestyle interventions, despite its importance for both internal and external validity. Creating and using fidelity measures can be complex and resource intensive. This study describes the development of the Lifestyle Implementation, Fidelity and Execution Monitor (LIFE Monitor), created for MULTI+, a multidisciplinary lifestyle-focused approach in treatment for people with mental illness. The overall study in which the LIFE Monitor was developed is an open cohort stepped wedge study. We established item objectives for 10 core components (i.e., essential elements of an intervention), and conducted item calibration (i.e., rating items on a gradient). We assessed fidelity through structured observations of 43 items. We investigated inter-rater reliability, item-level agreement, internal consistency and construct validity. The LIFE Monitor demonstrated sufficient inter-rater reliability, though there was high variability in agreement between coders. Internal consistency was generally low within core components, reflecting the multifaced nature of MULTI+. Although implementation duration was not statistically significantly associated with fidelity scores, the variability across clusters suggests that the LIFE Monitor captures the complexities of real-world implementation and has potential beyond research. This study provides practical guidance for developing fidelity measures for complex interventions. While the LIFE monitor requires further refinement, it shows promise as a pragmatic tool for monitoring in both research and clinical settings, including progress mapping and implementation guidance. ClinicalTrials.gov registration . Identifier: NCT04922749. Retrospectively registered June 3, 2021.