## 13.2 Hypothesis test objects: htest

R stores hypothesis tests in special object classes called htest. htest objects contain all the major results from a hypothesis test, from the test statistic (e.g.; a t-statistic for a t-test, or a correlation coefficient for a correlation test), to the p-value, to a confidence interval. To show you how this works, let’s create an htest object called height.htest containing the results from a two-sample t-test comparing the heights of male and female pirates:

# T-test comparing male and female heights
#  stored in a new htest object called height.htest
height.htest <- t.test(formula = height ~ sex,
data = pirates,
subset = sex %in% c("male", "female"))

Once you’ve created an htest object, you can view a print-out of the main results by just evaluating the object name:

# Print main results from height.htest
height.htest
##
##  Welch Two Sample t-test
##
## data:  height by sex
## t = -20, df = 1000, p-value <2e-16
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -15 -13
## sample estimates:
## mean in group female   mean in group male
##                  163                  177

Just like in dataframes, you can also access specific elements of the htest object by using the $ symbol. To see all the named elements in the object, run names(): # Show me all the elements in the height.htest object names(height.htest) ##  "statistic" "parameter" "p.value" "conf.int" "estimate" ##  "null.value" "alternative" "method" "data.name" Now, if we want to access the test statistic or p-value directly, we can just use $:

# Get the test statistic
height.htest$statistic ## t ## -21 # Get the p-value height.htest$p.value
##  1.4e-78

# Get a confidence interval for the mean
height.htest\$conf.int
##  -15 -13
## attr(,"conf.level")
##  0.95