1. Constructing Box Plots
Lesson 4
Constructing Box Plots

2. Warm up
3, 4, 8, 12, 7, 5, 4, 12, 3, 9, 11, 4, 14, 8, 2, 10, 3, 10, 9, 7
Find the minimum value, first quartile, median, third quartile and the maximum value.

3. Definition A box plot can be used to show how the values in a data set are distributed. 5 values are needed: the minimum value, first quartile, median, third quartile and the maximum value.

4. Method
Example: the numbers of runs scored by a softball team in 20 games are given:
3, 4, 8, 12, 7, 5, 4, 12, 3, 9, 11, 4, 14, 8, 2, 10, 3, 10, 9, 7

5. Order the data from least to greatest.
Identify the 5 needed values.
the minimum value, first quartile, median, third quartile and the maximum value

6. Draw a number line and plot a point above each of the 5 needed values.
Draw a box whose ends go through the 1st and 3rd quartiles, and draw a vertical line through the median.
Draw horizontal lines from the box to the min and max values.

7. Reflections
The lines that extend from the box in a box plot are sometimes called “whiskers”.
What part (lower, middle or upper) and about what percentage of the data does the box represent?
What part and about what percentage of the data does the whisker represent?
Which measures of spread can be determined from the box plot?
Calculate each measure.

8. Answers
Box: middle 50%; left whisker: lower 25%; right whisker: upper 25%
The range is the length of the entire box plot:
14 – 2 = 12
The IQR is the length of the box: 10 – 4 = 6

9. Assignment 4 1. Use the data to make a box plot.
25, 28, 26, 16, 18, 15, 25, 28, 26, 16
2. 2, 3, 4, 1, 1, 3, 4, 2, 6, 2, 2, 3, 2