1.标题：Standardization of risk ratios.
   作者：Miettinen, O. S. (Harvard School of Public Health, Boston, Mass. 02115).
   出版社：Am J Epidemiol 96: 383–388, 1972.
   链接：http://aje.oxfordjournals.org/cgi/content/abstract/96/6/383
2.标题：Confounding in epidemiologic studies: the Adequacy of the control groups as a measure of confounding.
   作者：PJ Wickramaratne, TR Holford - Biometrics.
   出版社：Biometrics, 43, 751-765 (1987)
   链接：http://links.jstor.org/sici?sici=0006-341X(198712)43%3A4%3C751%3ACIESTA%3E2.0.CO%3B2-3