King's College London

Background: Dissociative seizures (DS), also called psychogenic ‘non-epileptic’ seizures, are a distressing and disabling problem for many patients in neurological settings with high and often unnecessary economic costs. The CODES Trial evaluates a specifically-tailored psychological intervention with the aim of reducing seizure frequency and severity, and improving psychological well-being in adults with DS. The aim of this paper is to report in detail the quantitative and economic analysis plan for the CODES Trial, as agreed by the Trial Steering Committee.

Methods: The CODES Trial is a multicentre, pragmatic parallel group randomised controlled trial (RCT) to evaluate the clinical and cost-effectiveness of 13 sessions of cognitive behavioural therapy (CBT) plus standardised medical care (SMC) in comparison to SMC alone for adult outpatients with DS.

Discussion: The objectives and design of the trial are summarised, and the aims and procedures of the planned analyses are illustrated. The proposed analysis plan addresses statistical considerations such as maintaining blinding, monitoring adherence with the protocol, describing aspects of treatment and dealing with missing data. The formal analysis approach for the primary and secondary outcomes is described, as well as the descriptive statistics that will be reported. This paper offers transparency to the planned inferential analyses for the CODES Trial, prior to the extraction of outcome data. It also provides an update to the previously published trial protocol and guidance to those conducting similar trials.

Trial Registration
ISRCTN registry ISRCTN05681227 (registered 05 March 2014); ClinicalTrials.gov NCT02325544 (registered 15 December 2014).

Keywords
Statistical Analysis Plan, CODES Trial, nonepileptic seizures, dissociative seizures, cognitive behavioural therapy, randomised controlled trial.