OER Knowledge CloudJournal ArticleGrimaldi, Phillip J.Basu Mallick, DebshilaWaters, Andrew E.Baraniuk, Richard G.Open Educational Resources (OER) have been lauded for their ability to reduce student costs and improve equity in higher education. Research examining whether OER provides learning benefits have produced mixed results, with most studies showing null effects. We argue that the common methods used to examine OER efficacy are unlikely to detect positive effects based on predictions of the access hypothesis. The access hypothesis states that OER benefits learning by providing access to critical course materials, and therefore predicts that OER should only benefit students who would not otherwise have access to the materials. Through the use of simulation analysis, we demonstrate that even if there is a learning benefit of OER, standard research methods are unlikely to detect it.2019PLOS ONE31-14United States10.1371/journal.pone.0212508.s002https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212508yesaccess hypothesisOEROER efficacyresearch methodsjournal.pone_.0212508.pdfhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212508United States, North America