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Chapter 5: Bivariate Data
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CHAPTER 5
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Bivariate Data
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You should study the topics in this chapter if you need to review
or want to learn about
Relationships between two variables through graphical techniques
A numerical measure, referred to as linear correlation, which is used to
quantify the strength of a linear relationship between two variables
A modeling technique, referred to as regression analysis, which is used
to model a linear relationship between two variables
How to determine how well the model fits the data
How to analyze the errors or residuals produced by the linear model
5-1 Introduction
So far, you have dealt with single-variable or univariate data. In this
chapter, you will be introduced to quantitative bivariate or two-variable data.
That is, you will be analyzing data that are associated with two quantitative
variables. You will study the idea of association through graphical displays
as well as through correlation analysis. In addition, you will study how to
model the relationship between the two variables through regression analysis
and discuss how well the model fits the data.
The most common graphical display used to study the association between
two variables is called a
scatter plot
.
5-2 Scatter Plots
In simple correlation and regression studies, data are collected on two
quantitative variables to determine whether a relationship exists between the
two variables. If there is a significant correlation, one may use regression
techniques to determine a model for the data. However, before any