Azadbakht, Elena, et al. "Do Open Access Mandates Work? A Systematized Review of the Literature on Open Access Publishing Rates." Journal of Librarianship and Scholarly Communication, 11.1, (2023).
According to this study, although the majority of Open Access (OA) mandates described in scholarly literature were correlated with a subsequent increase in OA publishing, the presence of confounders and differing methods of collecting, analyzing data make it impossible to establish a causal link.