标题：Identification of Causal Effects Using Instrumental Variables
   作者：Joshua D. Angrist , Guido W. Imbens , Donald B. Rubin
   出版社：Journal of the American Statistical Association, Vol. 91, 1996
   电子链接：http://www.questia.com/googleScholar.qst;jsessionid=LLpB8yw9gTRVK0p0wz0GVP1nyqghlkJJXbnThXtqcfFyBhyRhZhk!921627548!-2106413634?docId=5002269527