Scatterplots

A scatterplot (or scatter graph) is a type of graph that helps determine if there is a relationship between two variables.

Example

Is there a relationship between the temperature and the sales (in $) of ice cream...?

A positive relationship is where one variable increases as the other increases as well.

Example 1

As the temperature increases, the sales (in $) of ice creams generally increases too.

A negative relationship is where one variable increases as the other variable decreases.

Example 2

As the number of missed classes increases, the exam score generally decreases.

The strength of the relationship depends on how well the data (points) fit to a mathematical model.

We usually try to identify a linear model (pattern) first before looking at other models.

We often refer to the 'model' as a trend.

We can go from a weak relationship (a lot of scatter and points do not follow any type of line or other model) to a strong relationship (very little scatter and points look like they follow a straight line or other model).