Kurata, Keiko, et al. "Monitoring the transition to open access through its mode of implementation: A principal component analysis of two surveys." PLoS One, 17.7, (2022).

This study examines how Open Access is implemented based on 2,368 randomly selected articles published in 2013 and 2,999 published in 2018 indexed in the Web of Science and searches in Google and Google Scholar in 2015 for articles published in 2013 and in 2020 for articles published in 2018.