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如果分配变量和代理变量(个人、公司等)是随机的，那么代理变量由于不能完全控制干预分配会使RDD在临界值处变得“和随机试验一样好”。例如，假设一项干预是通过一个考试，考试成绩必须在总分的50%以上。在这种情况下，只要成绩是随机的--随机的评分标准或随机的学生表现，这个例子都是一个有效的RDD设计。
如果分配变量和代理变量(个人、公司等)是随机的，那么代理变量由于不能完全控制干预分配会使RDD在临界值处变得“和随机试验一样好”。例如，假设一项干预是通过一个考试，考试成绩必须在总分的50%以上。在这种情况下，只要成绩是随机的,即无论这种随机性来源于随机的评分标准还是随机的学生表现，这个例子都是一个有效的RDD。
Students must not also be able to perfectly manipulate their grade so as to determine their treatment status perfectly. Two examples include students being able to convince teachers to "mercy pass" them, or students being allowed to retake the exam until they pass. In the former case, those students who barely fail but are able to secure a "mercy pass" may differ from those who just barely fail but cannot secure a "mercy pass". This leads to [[selection bias]], as the treatment and control groups now differ. In the latter case, some students may decide to retake the exam, stopping once they pass. This also leads to [[selection bias]] since only some students will decide to retake the exam.<ref name="Lee and Lemieux 2010">{{cite journal |last1=Lee |last2=Lemieux |title=Regression Discontinuity Designs in Economics |year=2010 |journal=[[Journal of Economic Literature]] |volume=48 |issue=2 |pages=281–355 |doi=10.1257/jel.48.2.281 |s2cid=14166110 |url=http://arks.princeton.edu/ark:/88435/dsp015138jd866 }}</ref>
Students must not also be able to perfectly manipulate their grade so as to determine their treatment status perfectly. Two examples include students being able to convince teachers to "mercy pass" them, or students being allowed to retake the exam until they pass. In the former case, those students who barely fail but are able to secure a "mercy pass" may differ from those who just barely fail but cannot secure a "mercy pass". This leads to [[selection bias]], as the treatment and control groups now differ. In the latter case, some students may decide to retake the exam, stopping once they pass. This also leads to [[selection bias]] since only some students will decide to retake the exam.<ref name="Lee and Lemieux 2010">{{cite journal |last1=Lee |last2=Lemieux |title=Regression Discontinuity Designs in Economics |year=2010 |journal=[[Journal of Economic Literature]] |volume=48 |issue=2 |pages=281–355 |doi=10.1257/jel.48.2.281 |s2cid=14166110 |url=http://arks.princeton.edu/ark:/88435/dsp015138jd866 }}</ref>