问题如下图：
选项：
A. 
B. 
C. 
解释：所以 如果样本服从正态分布 就可以用参数检验对吗？在不服从正态分布的情况下 样本大 可以参数检验 小的话只能非参数检验？
NO.PZ2017092702000147 问题如下 analyst is examining the monthly returns for two fun over one year. Both fun’ returns are non-normally stribute To test whether the mereturn of one funis greater ththe mereturn of the other fun the analyst cuse: A.a parametric test only. B.a nonparametric test only. C.both parametric annonparametric tests. B is correct. There are only 12 (monthly) observations over the one yeof the sample anthus the samples are small. Aitionally, the fun’ returns are non-normally stribute Therefore, the samples not meet the stributionassumptions for a parametric test. The Mann–Whitney U test (a nonparametric test) couluseto test the fferences between population means这道题检验的是两个均值之间的关系。如果对应的两个总体都是正态分布的话，那么我们需要使用t检验，也就是参数检验（对于t检验而言，参数就是自由度）。但这道题为非正态总体“Both fun’ returns are non-normally stribute，所以t检验就不能用了。这个时候只能使用非参数检验。 非正态分布，样本足够大不是也可以用Z检验吗？
NO.PZ2017092702000147 问题如下 analyst is examining the monthly returns for two fun over one year. Both fun’ returns are non-normally stribute To test whether the mereturn of one funis greater ththe mereturn of the other fun the analyst cuse: A.a parametric test only. B.a nonparametric test only. C.both parametric annonparametric tests. B is correct. There are only 12 (monthly) observations over the one yeof the sample anthus the samples are small. Aitionally, the fun’ returns are non-normally stribute Therefore, the samples not meet the stributionassumptions for a parametric test. The Mann–Whitney U test (a nonparametric test) couluseto test the fferences between population means这道题检验的是两个均值之间的关系。如果对应的两个总体都是正态分布的话，那么我们需要使用t检验，也就是参数检验（对于t检验而言，参数就是自由度）。但这道题为非正态总体“Both fun’ returns are non-normally stribute，所以t检验就不能用了。这个时候只能使用非参数检验。 如题，谢谢
NO.PZ2017092702000147 问题如下 analyst is examining the monthly returns for two fun over one year. Both fun’ returns are non-normally stribute To test whether the mereturn of one funis greater ththe mereturn of the other fun the analyst cuse: A.a parametric test only. B.a nonparametric test only. C.both parametric annonparametric tests. B is correct. There are only 12 (monthly) observations over the one yeof the sample anthus the samples are small. Aitionally, the fun’ returns are non-normally stribute Therefore, the samples not meet the stributionassumptions for a parametric test. The Mann–Whitney U test (a nonparametric test) couluseto test the fferences between population means这道题检验的是两个均值之间的关系。如果对应的两个总体都是正态分布的话，那么我们需要使用t检验，也就是参数检验（对于t检验而言，参数就是自由度）。但这道题为非正态总体“Both fun’ returns are non-normally stribute，所以t检验就不能用了。这个时候只能使用非参数检验。 是说，图里这三个检验，都需要前提是两个样本符合正态分布？
NO.PZ2017092702000147 a nonparametric test only. both parametric annonparametric tests. B is correct. There are only 12 (monthly) observations over the one yeof the sample anthus the samples are small. Aitionally, the fun’ returns are non-normally stribute Therefore, the samples not meet the stributionassumptions for a parametric test. The Mann–Whitney U test (a nonparametric test) couluseto test the fferences between population means我记得视频中讲test参数的都可以用参数检验，如果是test排序、符号等问题的才需要非参数检验。这道题是不是虽然提到了mean，但是本质是要看mean的大小（也就是类似排序或者符号）所以要用非参数检验？
是不是所有学过的参数检验的前提就是一定要符合正态分布？不符合的就是非参数检验，这样理解对吗？
