Abstract
RATIONALE: Developing a feasible and sensitive evaluation strategy for a new mental health service is a challenge that requires consideration of what a service is trying to achieve and what a 'good' outcome might look like. Perinatal mental illnesses are complex in their causes and treatment. Mother Baby Units provide specialist perinatal mental health care to parents experiencing mental illness in the perinatal period, with evaluations demonstrating clinical and social outcomes. There has however been remarkably little research on how MBUs achieve these outcomes. METHOD: This paper outlines the process and components of designing an evaluation plan for a new perinatal mental health unit, summarising outcome measures considered and the methodology of the evaluation strategy. RESULTS: A meaningful realist approach was designed. This innovative dualistic methodology is intended to develop theories of what might cause change while also considering what components of interventions parents experience as meaningful. CONCLUSION: Articulating the approach to evaluation provides a contribution to evaluation knowledge for others evaluating complex public health interventions. The relational nature of perinatal mental health experiences challenges individualistic approaches to care delivery, funding and evaluation. As part of service establishment, there is a need to consider what a 'good' outcome of care might be and to develop evaluation approaches that capture the relational components of recovery as well as the factors that support families to sustain change.