# Quartile

There are several quartiles of an observation variable. The first quartile, or lower quartile, is the value that cuts off the first 25% of the data when it is sorted in ascending order. The second quartile, or median, is the value that cuts off the first 50%. The third quartile, or upper quartile, is the value that cuts off the first 75%.

#### Problem

Find the quartiles of the eruption durations in the data set faithful.

#### Solution

We apply the quantile function to compute the quartiles of eruptions.

> duration = faithful\$eruptions     # the eruption durations
> quantile(duration)                # apply the quantile function
0%    25%    50%    75%   100%
1.6000 2.1627 4.0000 4.4543 5.1000

#### Answer

The first, second and third quartiles of the eruption duration are 2.1627, 4.0000 and 4.4543 minutes respectively.

#### Exercise

Find the quartiles of the eruption waiting periods in faithful.

#### Note

There are several algorithms for the computation of quartiles. Details can be found in the R documentation via help(quantile).