Economic evaluation of the Be-Prox anti-bullying intervention in Norwegian early childhood education and care settings: an exploratory partial within-trial cost-effectiveness analysis alongside a cluster randomised controlled trial

Background Experience of bullying during childhood incurs significant societal costs. While school-based anti-bullying programs have shown cost-effectiveness, there is a lack of economic evaluations of interventions aimed at reducing peer victimization at the preschool level. While the Be‑Prox intervention showed no effect on its primary outcome, reductions were observed in monthly victimization rates, motivating an economic evaluation of its potential value. Methods An exploratory partial within-trial cost-effectiveness analysis was conducted alongside a cluster randomized controlled trial (RCT) of the Be-Prox intervention in Norwegian early childhood education and care (ECEC) settings, from a provider and partial municipality perspective. The trial included 38 ECECs (19 intervention, 19 control) and 708 children aged 3–5 years. Costs were collected bottom-up through interviews and surveys, and control group costs were assumed to be zero. The incremental cost-effectiveness ratio (ICER) was calculated using the unweighted mean difference in ECEC-level proportions of children spared from negative acts between arms at follow-up. Uncertainty was assessed using ECEC level bootstrap resampling, summarized through cost-effectiveness planes and acceptability curves. Deterministic sensitivity analyses varied intervention costs by ± 1 SD, ± 1 standard error of the mean, and assignment of 10–30% of intervention costs to the control group. Results Total intervention costs were 1,889,031 Norwegian kroner (NOK) (165,270 EUR) across 19 ECECs. The primary ICER was 41,336 NOK (3,616 EUR) per child saved, based on a mean difference of 12.9% points between arms, corresponding to 45.7 children saved. A secondary, explorative ICER based on an adjusted odds ratio (0.40) from the effect paper was 26,330 NOK (2,304 EUR) per child saved, corresponding to 71.7 children saved. The primary ICER remained within a similar order of magnitude when intervention costs were varied by ± 1 SD (16,734 − 65,936 NOK; 1,464-5,770 EUR), was narrower under ± 1 SEM (35,691 − 46,980 NOK; 3,123-4,110 EUR), and reduced when control-group costs were assigned 10–30% of intervention costs (28,931–37,206 NOK; 2,531–3,255 EUR) under nonzero assumption. The probabilistic sensitivity analysis showed 97.3% of bootstrap draws in the north-east quadrant of the CE-plane, with the CEAC indicating 50% probability of cost-effectiveness at the primary ICER threshold, rising to 88% at 100,000 NOK (8,749 EUR) per child saved. Conclusions The Be-Prox intervention has the potential to be cost-effective. While exploratory, these findings provide the first economic evidence for bullying prevention at ECEC level and may inform early preventive strategies. Future research should adopt broader societal perspectives and longer follow-up to capture downstream cost savings. Trial registration The project is registered at ClinicalTrials with ID number NCT06040437, at 02.09.2023.