Evaluating a Behavioural Economics Nudge Intervention to Increase Consistent Condom Use Among Male Clients of Sex Workers in South Africa's Mining Sector: A Methodological Approach

Male clients of sex workers in South Africa's mining sector are a high-risk group for HIV transmission. Although HIV knowledge is often high, consistent condom use remains low. Behavioural economics 'nudge' strategies may help bridge this intention-behaviour gap, but there is a need for robust methodological frameworks to evaluate such interventions in this context. This methodology article aims to detail the study design for quantifying changes in consistent condom use following a behavioural economics nudge intervention. Its primary objective is to describe the design, implementation, and analytical plans for a field experiment with male clients in the mining sector of North West Province. The study employs a quasi-experimental, pre-post design with a comparison group. Participants are recruited from mining communities and allocated to an intervention or comparison arm. The intervention is a contextually tailored nudge bundle incorporating personalised feedback, default cues, and commitment devices. Data on condom use consistency, behavioural determinants, and socio-demographics are collected via structured surveys at baseline and follow-up. The primary outcome is the proportion reporting consistent condom use with sex workers in the preceding month. Analysis plans include difference-in-differences estimation and multivariable regression to isolate the intervention effect. As a methodology article, no empirical intervention results are presented. This section outlines methodological outputs, including the finalised study protocol, successfully piloted survey instruments, and a detailed description of the implemented nudge bundle. For instance, the commitment device component demonstrated a 92% uptake rate during piloting. This paper provides a comprehensive methodological blueprint for evaluating a behavioural economics intervention in a complex, real-world setting. The detailed approach is intended to improve the rigour and replicability of nudge-based HIV prevention research among key populations in Africa. Future research should apply and adapt this methodological framework in similar high-risk populations and settings to further test the efficacy of behavioural nudges in HIV prevention. behavioural economics, nudge, HIV prevention, condom use, sex workers, mining sector, methodology, South Africa This article contributes a detailed methodological framework for designing and evaluating behavioural economics interventions aimed at increasing consistent condom use among a high-risk population in an African setting.