In the US, HE models are often developed by for-profit economic consultants, academic researchers, or health economics and outcomes research experts within life sciences companies [13, 14]. Key model assumptions, specifications, and data inputs are often determined by technical experts, and access to key assumptions or data inputs in the HE models can be limited due to intellectual property concerns [13, 15]. Additionally, HE models seldom consider or incorporate direct patient perspectives and inputs, and they might fail to capture real-world patient experiences valued by decision makers [11, 16]. Perspectives from external stakeholders are often sought ex post and used as contextual inputs or considerations rather than being consistently incorporated into models. The lack of transparency about key modeling decisions and limited stakeholder participation in the model development process can lead to misalignment between model design and decision needs of end users . These limitations cause relevant decision makers to question the credibility and relevance of cost-effectiveness estimates and, ultimately, the ability of models to inform HTA in meaningful ways [17, 18].
In July 2020, IVI launched its third Open-Source Value Project initiative to build an HE model to support HTA for major depressive disorder (MDD). We chose MDD due to its prevalence, significant societal burden, and broad interest among stakeholders who are looking for better treatments and more cost-effective resource allocation [19, 20]. As a first step, IVI convened a 20-member Advisory Group1 (AG) consisting of patients (n = 5), employers (n = 5), clinicians (n = 5), innovators (n = 3), payers (n = 2), and researchers (n = 2) to weigh in throughout the modeling process.
To date, the AG has provided feedback on the model’s conceptual framework  as well as the model design, including identifying (1) decision needs (model objectives); (2) gaps in existing economic models; (3) data sources for model inputs; and (4) the most appropriate analytic framework when multiple approaches exist. Feedback was provided through group meetings, surveys, emails, and individual discussions. In prioritizing feedback from the AG, we solicited additional insights from patients and employers, two traditionally under-represented stakeholder groups in the HE modeling process [11, 12, 22].