1. Allison, Paul. 2002. Missing data. Thousand Oaks, CA: Sage.
2. Allison, Paul. 2012. Handling missing data by maximum likelihood. http://statisticalhorizons.com/wp-content/uploads/MissingDataByML.pdf . Accessed 30 Nov 2016.
3. Astin, Alexander W. 1993. What matters in college: Four critical years revisited. San Francisco: Jossey-Bass.
4. Baxter Magolda, Marcia B. 1992. Knowing and reasoning in college: Gender-related patterns in students’ intellectual development. San Francisco: Jossey-Bass.
5. Bielo, James. 2011. Emerging evangelicals. New York: NYU Press.