Dot plots and stem-and-leaf plots are used to represent numerical data. They are suitable for small to moderate sized data sets.
Dot plots are very good for highlighting outliers and clusters in the data. This will be discussed more in the next chapter.
Dot plots
A dot plot is used for organising and displaying numerical data. It is good for small sets of discrete numerical data, but can also be used for data that is categorical.
In a dot plot, each individual value, or score, is represented by a single dot, displayed above a horizontal number line. When data values are identical, the dots are stacked vertically.
- To correctly display the distribution of the data, the dots must be evenly spaced in columns above the number line
- The scale on the number line must be evenly spaced
- A dot plot does not have a vertical axis
- The dot plot should be appropriately labelled
Practice questions
Question 1
Here is a dot plot of the number of goals scored in each of Bob’s soccer games.
How many times were five goals scored?
Which number of goals were scored equally and most often?
$1$1
A$0$0
B$4$4
C$3$3
D$2$2
E$5$5
FHow many games were played in total?
Question 2
The goals scored by a football team in their matches are represented in the following dot plot.
Complete the following frequency distribution table.
Goals scored Frequency $0$0 $\editable{}$ $1$1 $\editable{}$ $2$2 $\editable{}$ $3$3 $\editable{}$ $4$4 $\editable{}$ $5$5 $\editable{}$