The UK national evaluation of the development and impact of Early Intervention Services (the National EDEN studies): study rationale, design and baseline characteristics.

Aims: National EDEN aims to evaluate the implementation and impact on key outcomes of somewhat differently configured Early Intervention Services (EIS) across sites in England and to develop a model of variance in patient outcomes that includes key variables of duration of untreated psychosis (DUP), fidelity to the EIS model and service engagement. The cohort is being followed up for two further years as patients are discharged, to observe the stability of change and the impact of the discharge settings.

Methods: A longitudinal cohort study of patients with a first episode of a psychosis, managed by EIS in six services across England. Patients are followed up 12 months after inception, then up to 2 years following discharge. Measures of DUP, psychosis, social functioning and relapse were taken. User and carer experience of EIS were monitored over time; as was the fidelity of each EIS to national guidelines. Service use is costed for a health economic evaluation.

Results: 1027 people consented to the study of which 75% were successfully followed up at 12 months, with almost 100% data on treatment, relapse and recovery and service use.

Conclusions: National EDEN is the largest cohort study of young people with psychosis receiving care under EIS. It will be able definitively to indicate whether this major investment in the United Kingdom in EI is achieving meaningful change for its users in practice and provide indications concerning who does well under this approach and who does not, and the long-term stability of any improvements.