signtest abnormal_return=0 if dif==0<br/><br/>Sign test<br/><br/>        sign |    observed    expected<br/>-------------+------------------------<br/>    positive |         416       450.5<br/>    negative |         485       450.5<br/>        zero |           0           0<br/>-------------+------------------------<br/>         all |         901         901<br/><br/>One-sided tests:<br/>  Ho: median of abnormal~n - 0  = 0 vs.<br/>  Ha: median of abnormal~n - 0  > 0<br/>      Pr(#positive >= 416) =<br/>         Binomial(n = 901, x >= 416, p = 0.5) =  0.9902<br/>问题1：这儿说明什么<br/><br/>  Ho: median of abnormal~n - 0  = 0 vs.<br/>  Ha: median of abnormal~n - 0  < 0<br/>      Pr(#negative >= 485) =<br/>         Binomial(n = 901, x >= 485, p = 0.5) =  0.0117<br/>问题2：这儿说明什么<br/><br/>Two-sided test:<br/>  Ho: median of abnormal~n - 0  = 0 vs.<br/>  Ha: median of abnormal~n - 0  != 0<br/>      Pr(#positive >= 485 or #negative >= 485) =<br/>         min(1, 2*Binomial(n = 901, x >= 485, p = 0.5)) =  0.0234<br/>问题3：这儿说明什么。<br/><br/>一直没有弄明白，中位数检验.各位指导下，谢谢了。<br/><br/>