Compare Two Means

Are they statistically the same?

x <- rnorm(100)
y <- rnorm(100,1)

boxplot(x,y)

t.test(x,y)

## 
##  Welch Two Sample t-test
## 
## data:  x and y
## t = -5.8207, df = 190.708, p-value = 2.444e-08
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -1.1579460 -0.5717871
## sample estimates:
## mean of x mean of y 
## 0.1624531 1.0273196

# R will say no (most of the time)

Compare mean with a number (Is the true mean 0?)

t.test(x,mu=0)

## 
##  One Sample t-test
## 
## data:  x
## t = 1.7239, df = 99, p-value = 0.08784
## alternative hypothesis: true mean is not equal to 0
## 95 percent confidence interval:
##  -0.02452888  0.34943501
## sample estimates:
## mean of x 
## 0.1624531

# R will say yes (most of the time)