1. Astin, A. The methodology of research on college impact (I).Sociology of Education 1970,43 223?254.
2. Astin, A.Four critical years: effects of college on beliefs, attitudes, and knowledge. San Francisco: Jossey-Bass, 1977.
3. Astin, A., and Panos, R.The educational and vocational development of college students. Washington, D.C.: American Council on Education, 1969.
4. Bean, J. Dropouts and turnover: the synthesis and test of a causal model of student attrition.Research in Higher Education 1980,12 155?187.
5. Bowen, H. R.Investment in learning: the individual and social value of American higher education. San Francisco: Jossey-Bass, 1977.