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CHAPTER 5
Two Quantitative Variables’ Relationship
3 Tools:
Scatterplot –
a twodimensional graph of data
values
Regression equation –
an equation that describes the average relationship between a
quantitative response variable and an explanatory variable
Correlation –
a statistic that measures the strength and direction of a linear relationship
between two quantitative variables
Scatterplots
The response variable is often called the
dependent variable
and is plotted along the yaxis of the graph.
The explanatory variable is often called the
independent variable
and is plotted along the xaxis of the graph.
Two variables have a
positive association
when the values of one variable tend to increase and the values of the other
variable increase.
Two variables have a
negative association
when the values of one variable tend to decrease as the values of the other
variable increase.
If a straight line describes the general pattern of the graph, the two variables may have a linear relationship.
Does the diameter of a certain type of tree predict the volume of the trunk of the tree?
This scatterplot is an example of a positive linear relationship.
What effect does temperature have on the elongation of a certain type of metal rod?
This scatterplot is an example of a curvilinear relationship.
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Outliers in Scatterplots
When considering two variables, an outlier is a point that has an unusual combination of data values.
Regression Equation
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This note was uploaded on 02/03/2010 for the course STAT 200 at Pennsylvania State University, University Park.
 '08
 BARROSO,JOAOR
 Statistics

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