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Scatterplot
A scatterplot is a graphic tool used to display
the relationship between two
quantitative
variables.
A scatterplot consists of an X axis (the horizontal axis), a
Y axis (the vertical axis), and a series of dots.
Each dot on the scatterplot represents one observation
from a data set. The position of the dot on the scatterplot
represents its X and Y values.
Consider the example below. On the left, a
table shows the height and the weight of five starters on a high
school basketball team. On the right, the same data are displayed
in a scatterplot.
| Height, inches |
Weight, pounds |
| 67 |
155 |
| 72 |
220 |
| 77 |
240 |
| 74 |
195 |
| 69 |
175 |
|
|
|
Each player in the table is represented by a dot on the scatterplot.
The first dot, for example, represents the shortest, lightest player.
From the scale on the X axis, you see that the shortest player is 67
inches tall; and from the scale on the Y axis, you see that he/she
weighs 155 pounds. In a similar way, you can read the height and
weight of every other player represented on the scatterplot.
Scatterplots are helpful in understanding patterns in
bivariate data
. For example, the above scatterplot shows that the
relationship between height and weight is linear, strong, and has a
positive slope.