1. Baum S, Ma J, Payea K. Trends in public higher education: enrollment, prices, student aid, revenues, and expenditures. New York, NY: College Board Advocacy & Policy Center; 2012.https://trends.collegeboard.org/sites/default/files/trends-2012-public-higher-education-expenditures-brief.pdf. Accessed February 1, 2019.
2. Bureau of Labor and Statistics. College tuition and fees increases 63 percent since January 2006. 2016.https://www.bls.gov/opub/ted/2016/college-tuition-and-fees-increase-63-percent-since-january-2006.htm. Accessed March 1, 2019.
3. Fixing the Broken Textbook Market: How Students Respond to High Textbook Costs and Demand Alternatives;Senack,2014
4. Why openness in education?;Wiley,2012
5. Online and campus college students like using an open educational resource instead of a traditional textbook;Lindshield;J Online Learn Teach,2013