Box Plots and Quartiles

Box Plots/Box and Whiskers

It is another way to represent data.  We have already used Dot Plots and Histograms to represent data.  Box Plots are an easy way to show if a number is above the middle of data or below the middle of data.

5 Number Summary

We use the 5 number Summary (5 special data number) to create and help interpret data from a box plot.  The 5 number summary includes:  Minimum, Maximum, (Q1) Quartile 1 or Lower Quartile, (Q2) Median, and (Q3) Quartile or Upper Quartile.

Parts of a Box Plot

• Min – Minimum: Smallest number of the Data Set

• Q1 – Lower Quartile:  The median of the lower half of the data

• Q2 – Median:   Middle number of the set of data

• Q3 – Upper Quartile:  The median of the upper half of the data

• Max – Maximum:  Largest number in the data set

• Interquartile Range (IQR): Q3 – Q1

Multiple Choice

What is the Median (Q2) of this Box Plot?

• 80

• 82

• 81.5

Multiple Choice

Find the Interquartile Range (range of the "box") for this Box Plot. (Hint: Q3 - Q1)

• 92 - 77 = 15

• 77 - 92 = -15

• 92 + 77 = 169

• 92 - 77 = 25

Quartiles

• Quartiles divide the data set into four equal parts.

• 25% each

Median

• Divides the data set into two halves

• 50% of the data numbers are below this number

• 50% of the data numbers are above this number

Multiple Choice

Given the Box Plot: Identify the Lower Quartile.

• 33.5

• 33

• 34

• 34.5