Key Concepts

• A box plot is a graph that shows the minimum, first quartile, median, third quartile, and maximum in a data set.
• Box plots that use the same scale can be used to compare distributions.
• The length of the box is the same as the interquartile range.

Glossary

box plot: a graph that gives a quick picture of the middle 50% of the data

first quartile: the value that is the median of the of the lower half of the ordered data set

interquartile range (IQR): the range of the middle 50% of the data values. The IQR is found by subtracting the first quartile from the third quartile

median: a number that separates ordered data into halves; half the values are the same number or smaller than the median and half the values are the same number or larger than the median. The median may or may not be part of the data.

outlier: an observation that does not fit the rest of the data

quartiles: the numbers that separate the data into quarters; quartiles may or may not be part of the data. The second quartile is the median of the data.