1Sackett DL, Richardson WS, Rosenberg W,Haynes RB. Evidence - based Medicine:How to practice and teach EBM. New York:Churchill Livingston. 1997.
2Guyatt GH, Sackett DL, Cook DJ for the Evidence- based Medicine Working Group.Users' guides to the medical literature. Ⅱ .How to use an article about therapy or prevention. A Are the results of the study valid? JAMA 1993: 270: 2598-601.
