3.1A Scatterplots and Correlation Explanatory and Response Variables We think that smoking causes a decrease in life expectancy. Notice the two variables, underlined. There is a relationship between the two variables, but each play a different role. Life expectancy is a response variable, while the number of cigarettes smoked is an explanatory variable. The National Student Loan Survey provides data on the amount of debt for recent college graduates, their income, and how stressed they feel about college debt. A sociologist looks at the data with the goal of using amount of debt and income to explain the stress caused by college debt. Which variable is the explanatory variable? Which variable is the response variable? Displaying Relationships: Scatterplots The most useful graph for displaying the relationship between two ____________________ variables is a scatterplot. Each individual in the data appears as a point in the graph. Response Variable Explanatory Variable How to Make a Scatterplot: 1. 2. 3. x-axis:_____________________________ y-axis:_____________________________ How to Interpret a Scatterplot: As in any graph of data, look for the overall pattern and for striking departures from that pattern. 1. Direction a. Positive Association – Low-Low and High-High moves from low left to upper right, positive slope b. Negative Association – Low-High and High-Low moves from upper left to low right, negative slope 2. Form – look for curves and clusters (is it a line or curve?) 3. Strength – determined by how closely the points follow a clear form (is it an obvious line or curve? 4. Outliers **If you are asked to make a scatterplot, be sure to label and scale both axes! Don’t just copy it down **
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3.1A Scatterplots and Correlation
Explanatory and Response Variables
We think that smoking causes a decrease in life expectancy. Notice the two variables, underlined. There is a relationship
between the two variables, but each play a different role. Life expectancy is a response variable, while the number of
cigarettes smoked is an explanatory variable.
The National Student Loan Survey provides data on the amount of debt for recent college graduates, their income, and
how stressed they feel about college debt. A sociologist looks at the data with the goal of using amount of debt and
income to explain the stress caused by college debt.
Which variable is the explanatory variable?
Which variable is the response variable?
Displaying Relationships: Scatterplots
The most useful graph for displaying the relationship between two ____________________ variables is a scatterplot.
Each individual in the data appears as a point in the graph.