Comparing Data with Dot Plots
A dot plot uses dots over a number line to show frequency of data.
When using dot plots to compare two sets of data,
1. Use the SAME scale!
2. Stack the dot plots vertically!
Example: Roscoe is comparing the heights of basketball players to soccer players. He believes that
the mean height of the basketball players will be greater than the mean height of the soccer players.
He also believes that there will be more variation (spread) in the heights of soccer players.
Roscoe’s data:
Roscoe’s data ranges from 65 in. to 84 in., so his dot plots will use a scale of 65 to 84.
Looking at these dot plots, what can you infer about…
1) Mean height of soccer vs. basketball players?
2) The variation in heights of soccer vs. basketball
players?
Why would you NOT display Roscoe’s data like the dot plots below?
Example 1:
Height of Soccer Players (in)
Height of Basketball Players (in)
Example 2:
Comparing Data with Dot Plots ~ Practice
Principal Skinner drew these line plots to
compare class sizes of 6th graders
and 7th graders at his school.
Number of Students in 6th Grade Classes
Number of Students in 7th Grade Classes
1) What do you notice about the SCALES on the
number lines of the dot plots?
2) Which grade has the higher average class size? ____
How do you know this, without actually calculating
the mean?
3) What can you infer about the variability of class sizes
in 6th grade vs. 7th grade?
Dr. K wanted to compare the amount of time per week his peers spend reading books to the
amount of time they spend watching TV. The data he collected is as follows:
Person
A B C D E F G H I J
Weekly Hrs. Reading 5 4 10 7 6 7 6 9 8 8
Weekly Hrs. of TV
10 12 14 10 20 5 14 13 9 2
1) Plot this data on the double dot plot below. Remember to give your dot plots titles, and
pay careful attention to the scale!
2) What inferences can you make about the mean hours spent reading vs. watching TV?
3) What inferences can you make about the variation in the data sets above?