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Introduction: Loneliness has emerged as a global public health issue and is linked to serious health conditions. One approach to tackle loneliness is nature-based social prescribing (NBSP), referring people experiencing loneliness to non-medical group-based activities held in a natural setting. We aim to outline the framework of the cost-effectiveness analysis along the RECETAS trial in Spain to evaluate the Friends in Nature (FiN) NBSP intervention for reducing loneliness among adults. 316 participants were randomized to the intervention, organized nature-based group activities, or control group, receiving a menu of unsupported nature-based community resources, by May 2024 as part of the RECETAS project [1], [2].

State of the art: We will conduct cost-effectiveness, cost-utility, and cost-capability analyses alongside the randomized controlled trial in Barcelona.

Concept: FiN is a NBSP intervention, which involves referring lonely individuals to a facilitator-led, group-based nature-based process over nine weeks, providing access to nearby nature-based community resources together with group members. The treatment group will be compared to usual care (UC), which includes controls who receive a list of nature-based activities. Effectiveness will be measured by changes in loneliness using the De Jong Gierveld Loneliness Scale, health-related quality of life through the EQ-5D-5L questionnaire, and capability obtained from the ICECAP-A questionnaire. The economic evaluation will be conducted from a societal perspective including direct healthcare costs, as well as indirect, informal, and intervention-related costs. Data on health outcomes and healthcare resource utilization will be collected at baseline, and at three-, six-, and twelve-month follow-ups using the previously developed health economic questionnaire and electronic medical records. Costs of the NBSP intervention and control group will be obtained directly from the trial. Direct healthcare costs will be calculated using published unit prices from Catalan Department of Health [3] and BOT PLUS database for medications and pharmaceutical products [4]. Indirect costs for informal care and due to productivity losses will be calculated using the average salary from the Spanish National Statistics Institute and the minimum wage derived from the Spanish Ministry of Labor and Social Economy [5], respectively. The incremental cost-effectiveness ratio, cost-capability ratio, and cost-utility ratio will be calculated by dividing the cost differences between the intervention and control groups by the corresponding differences in effectiveness, capability, and utility measures. As the Spanish National Health System does not have an explicit national willingness-to-pay (WTP) threshold, cost-acceptability curves will be provided and commonly used estimates of an appropriate WTP will be applied to inform decisions on cost-effectiveness.

Implementation: Upon trial completion, we will conduct the health economic evaluation of the FiN NBSP intervention compared to UC targeting individuals experiencing loneliness aligned with our previously developed study protocol.

Lessons learned: By publishing our study protocol, the research process is made transparent and reproducible. This helps to minimize bias in interpreting the results and conclusions, ensuring a strong evidence base. As a result, decision makers can offer objective, evidence-driven recommendations to support the implementation of NBSP.

The RECETAS project received funding from the European Union’s Horizon 2020 Research and Innovation program under grant agreement No 945095.

The authors declare that a positive ethics committee vote has been obtained.

Literatur

[1] Litt JS, Coll-Planas L, Sachs AL, Rochau U, Jansson A, Dostálová V, et al. Nature-based social interventions for people experiencing loneliness: the rationale and overview of the RECETAS project. Cities & Health. 2024:1-14.
[2] Coll-Planas L, Carbo-Cardena A, Jansson A, Dostalova V, Bartova A, Rautiainen L, et al. Nature-based social interventions to address loneliness among vulnerable populations: a common study protocol for three related randomized controlled trials in Barcelona, Helsinki, and Prague within the RECETAS European project. BMC Public Health. 2024;24(1):172.
[3] Diari Oficial de la Generalitat de Catalunya. ORDEN SLT/63/2020, de 8 de marzo, por la que se aprueban los precios públicos del Servicio Catalán de la Salud. 2020 [cited 2025 Mar 26]. Available from: https://dogc.gencat.cat/es/document-del-dogc/index.html?documentId=873353
[4] BOT PLUS. Drug and Parapharmacy Database (Healthcare Professionals). [cited 2025 Mar 26]. Available from: https://www.farmaceuticos.com/botplus/
[5] Real Decreto 99/2023, de 14 de febrero, por el que se fija el salario mínimo interprofesional para 2023. 2023 [cited 2025 Mar 26]. Available from: https://www.boe.es/eli/es/rd/2023/02/14/99