Box-and-Whisker Plots

A box-and-whisker plot shows the distribution of data. It separates data into four equal parts

The box contains the median, the upper quartile, and the lower quartile. A vertical line is drawn through the median

The whiskers extend from the quartiles to the extreme values

The middle half of the data is represented by a ‘box’ with a vertical line at the median. The lower quartile and upper quartile are represented by ‘whiskers’ that extend to the smallest and largest values

A long whisker or box indicates that the data in that quartile or quartiles have a greater range. A shorter whisker or box indicates that the data in that quartile or quartiles have a lesser range

The interquartile range is the difference between the lower quartile and the upper quartile

Outliers are data values that are more than 1.5 times the interquartile range from the quartiles. They are not included in the whiskers of the box-and-whisker plots

The lower whisker is drawn from the lower quartile to the least value that is not an outlier

The upper whisker is drawn from the upper quartile to the greatest value that is not an outlier

The median divides the data set into two equal parts

The median and the quartiles divide the data set into 4 equal parts

One fourth data set lies between the lower/upper quartile and the median

The length of the whiskers and the length of the box in the box-and-whisker plot of the data indicate the spread and the variability of data

The length of the box-and-whisker plot indicates the interquartile range of the plot

A shorter length of the whiskers and the box indicates less variation in the data