## Boxplot

A*boxplot*is a schematic presentation of summary statistics: a measure of center (sample median), a measure of variation (IQR between lower and upper quartiles), and the largest and smallest data. It also indicates the symmetry or skewness of the distribution and the presence of possible outliers. The plot will be displayed.

A box in the middle of boxplot
stretches from the lower quartile `Q1` (the 25-percentile)
to the upper quartile `Q3` (the 75-percentile).
The median `Q2` is shown as a line across the box.
Therefore, 1/4 of the observations lies between this
line and the right of the box and 1/4
of the observation between this line and the left of the box.
Straight lines (either horizontal or vertical)
are called *whiskers*, stretching out from
the ends of the box to the largest and smallest value, `Q0` and `Q4`.
In the computer-generated boxplot potential outliers will be
indicated separately from whiskers.

The data of one variable are often grouped by another categorical variable.
Such a categorical variable is often referred as ``factor,''
and its values are called ``levels.''
The presentation of *side-by-side boxplots* is quite useful for comparing
the data from different groups (i.e., different levels).

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