Economic evaluation protocol of the Ntshembo (Hope) Trial (RCT) in rural and urban South Africa: an intervention to optimise adolescence body mass index (BMI) pre-conception to address the triple burden of malnutrition

South African adolescent girls face a triple burden of malnutrition, undernutrition alongside overweight/obesity, and micronutrient deficiencies, heightened risk factors for Non-Communicable Diseases (NCDs). The Ntshembo trial is a South African Randomised Controlled Trial (RCT) that utilises Community Healthcare Workers to support at-risk adolescent girls (14–19 years old) in improving their body mass index (BMI) through nutrition- and behaviour-based interventions, combined with a household conditional cash transfer. The intervention aims to optimise BMI and, by doing so, reduce both individual and transgenerational risk for metabolic diseases like type-2 diabetes. This protocol outlines the methods that will be used alongside the intervention to conduct an economic evaluation, including a cost-effectiveness analysis, of the Ntshembo (Hope) RCT. The intervention cost will be estimated from the provider and societal perspectives. The cost of implementing the intervention in an RCT setting (scenario 1) and of replicating the intervention in a non-research context (scenario 2) will be modelled. An activity-based approach will be used to identify and cost the activities involved in implementing both the intervention and the comparator (standard of care). The cost components of each activity will be identified and estimated through three sources: (1) expenditure records from the Ntshembo trial, (2) primary data collected through key informant interviews with implementation staff, and (3) participant questionnaires. Additional cost data will be sourced from the Department of Health (DoH) budget reports and published literature to estimate the value of resources used but not directly paid for (opportunity cost). The economic evaluation will consist of three elements: (i) a cost-consequence analysis which compares the cost versus benefits of the intervention, (ii) the incremental cost-effectiveness ratios (ICERs) using the primary and secondary outcomes, and (iii) the cost per Disability-adjusted Life Years (DALYs) averted by the intervention. DALYs averted over the life course will be modelled using the change in BMI and information on confounders using a Markov model. The long-term benefits, including (depending on the nature and magnitude of benefits observed) later-life labour market outcomes, will be modelled. Probabilistic sensitivity analyses will be performed to understand uncertainty and evaluate the robustness of the results. This economic evaluation study is part of a larger project: The Ntshembo (Hope) trial (see the economic evaluation section of the Ntshembo protocol). The larger study is approved by the Human Ethics Research Committee of the University of the Witwatersrand, Johannesburg, South Africa (M211061) and of the University of Cambridge (HBREC.2022.07). The Ntshembo trial is registered with the Pan-African Clinical Trials Registry. identifier: PACTR202201638897606. Registered on 1st August 2022, https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=14656