1.标题：Identifiability exchangeability a  epidemiologic confounding
   作者：GREENLAND and ROBINS
   出版社：Int. J. Epidemiol..1986; 15: 413-419
   链接：http://ije.oxfordjournals.org/cgi/reprint/15/3/413
2.标题：Case-Control Studies - Design, Conduct, Analysis.
   作者：Schlesselman J.J.(1982)
   出版社：New York, Oxford University Press, 354 p.
   链接：http://www.google.com/books?hl=zh-CN&lr=&id=5OkyFkYOn0QC&oi=fnd&pg=PA3&dq=%22Schlesselman%22+%22Case-control+studies:+design,+conduct,+analysis%22+&ots=pcag9-YwCA&sig=ddUuFSiNwzLdiy6a8ykup7AfQ3w