两配对t检验p值= NA和t = NaN的

Question

我愿做以下配对t检验：

str1<-' ENSEMBLE 0.934 0.934 0.934 0.934 ' 
    str2<-' J48 0.934 0.934 0.934 0.934 ' 

    df1 <- read.table(text=scan(text=str1, what='', quiet=TRUE), header=TRUE) 
    df2 <- read.table(text=scan(text=str2, what='', quiet=TRUE), header=TRUE) 

t.test (df1$ENSEMBLE, df2$J48, mu=0 , alt="two.sided", paired = T, conf.level = 0.95) 

我得到以下结果：

Paired t-test 

data: df1$ENSEMBLE and df2$J48 
t = NaN, df = 3, p-value = NA 
alternative hypothesis: true difference in means is not equal to 0 
95 percent confidence interval: 
NaN NaN 
sample estimates: 
mean of the differences 
         0 

为什么我懂吗？

Answer 1

这是因为数据集完全一样。

df2[1,1] <- .935 

t.test (df1$ENSEMBLE, df2$J48, mu=0 , alt="two.sided", paired = T, conf.level = 0.95) 

Paired t-test 

data: df1$ENSEMBLE and df2$J48 
t = -1, df = 3, p-value = 0.391 
alternative hypothesis: true difference in means is not equal to 0 
95 percent confidence interval: 
-0.0010456116 0.0005456116 
sample estimates: 
mean of the differences 
      -0.00025 

Answer 2

你的两个向量是完全一样的。两组没有差异，因此没有标准误差。所以你的答案是undefined