I really liked the ease of reading this study by John Hilton III. I made a quick summary to help me better understand his methods and conclusions. I realize that this research was conducted several years ago and is now surpassed by new research, but it was good to see the review of the studies that were made at the beginnings of the wider use of OER.
https://spark.adobe.com/page/2nhUIOUstzotI/
Reference:
Hilton, J. Open educational resources and college textbook choices: a review of research on efficacy and perceptions. Education Tech Research Dev 64, 573–590 (2016). https://doi.org/10.1007/s11423-016-9434-9
#intro2opened