# Data from W.S. Gosset's 1908 paper on the t-test.
# Two different sleeping drugs were taken by two groups of patients.
 
# The variable "extra" is the increase in hours of sleep on the groups 
# (consisting of 10 patients each).
# The variable "group" gives the labels for which drug each patient took.

# The sleeping data is a built-in data set in R,
# so we can simply load it and attach it with the following:

data(sleep); attach(sleep)

# Viewing the data:
print(extra)
print(group)

# Alternately, we could type in the variables in the usual way:
#extra <- c(0.7,-1.6,-0.2,-1.2,-0.1,3.4,3.7,0.8,
#0.0,2.0,1.9,0.8,1.1,0.1,-0.1,4.4,5.5,1.6,4.6,3.4)
#group <- c(1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2)

boxplot(extra ~ group)

# Do the spreads seem equal across groups?

# Assuming equal variances:
t.test(extra ~ group, var.equal=TRUE)

# Not assuming equal variances:
t.test(extra ~ group)