Background
Reducing the detrimental life course impacts of childhood bullying is a key preventative public health approach. KiVa is a complex universal anti-bullying programme found effective for reducing bullying in schools in Finland and Italy.
In addition to KiVa being a complex intervention, schools can be considered complex systems.

Economic evaluation therefore requires careful conceptual planning and a wide evaluative lens to provide relevant value for money evidence. Here we outline an ongoing economic evaluation of KiVa, conducted alongside the Stand Together randomised controlled trial (RCT), to explore the cost-effectiveness of KiVa for
reducing bullying in UK primary schools. We present methodological challenges and key questions for HESG colleagues.

Methods
The Stand Together two-arm pragmatic cluster RCT investigated the effectiveness and costeffectiveness of KiVa compared to usual practice over one academic year. The trial recruited approximately 11,500 7-to-11-year-olds in 118 primary schools across England and Wales, randomised on 1:1 basis.

Our proposed evaluation includes;
i) a cost-utility analysis estimating the incremental cost per quality-adjusted life year (QALY) gained, calculated using pupil self-reported health-related quality of life (HQoL) assessed through the Child Health Utility 9D (CHU-9D) measure;
ii) a cost-effectiveness analysis estimating the incremental cost per bullying incident avoided (BIA), calculated using pupil self-reported bullying-victimisation assessed through the Olweus Bully/Victim questionnaire, and;
iii) a cost-consequence analysis conducted comparing costs with a wider range of pupil and teacher outcomes.

All outcomes were assessed at baseline and 12-month follow-up and the above analyses are currently underway. Cost calculations include time and resources required to implement KiVa and usual practice, collected via surveys and interviews with school staff. Sensitivity analyses will explore assumptions and uncertainty.

Methodological challenges
As with all public health interventions, there are methodological challenges involved in evaluating the UK Stand Together trial. These include defining an appropriate comparator, perspective, and time horizon, identifying and quantifying relevant outcomes and costs, the consideration of equity, and the practical challenge of collecting sufficient data from schools and parents to accurately quantify costs and benefits. We welcome HESG comment on these
challenges.