2 Samples T-test

Default command line for 2 samples T-test

t.test(x, y, alternative = "two.sided", var.equal = FALSE)

x,y: numeric vectors

alternative: the alternative hypothesis. Allowed value is one of “two.sided” (default), “greater” or “less”.

var.equal: a logical variable indicating whether to treat the two variances as being equal. If TRUE then the pooled variance is used to estimate the variance otherwise the Welch test is used.

Example: A postgraduate students would like to investigate 
if there is difference in the mean number of leaves 
per plant from two different Shorea species grown under 
same light intensity. She sampled from 12 individuals 
for each species. Assume that the variances are equal.

2 samples T-test

x<-c(12,12,13,14,15,16,12,13,12,13,13,12)
y<-c(8,9,11,11,12,13,13,12,12,13,12,12)
t.test(x, y, alternative = "two.sided", var.equal = TRUE)

## 
##  Two Sample t-test
## 
## data:  x and y
## t = 2.6846, df = 22, p-value = 0.01354
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  0.3601815 2.8064852
## sample estimates:
## mean of x mean of y 
##  13.08333  11.50000