Chapter 2
Examining Relationships
Chapter 2
1
Recall  Exploratory Data Analysis
•
Use some statistical tools to describe some of the
main features
of the dataset. This process is
known as
exploratory data analysis
.
•
Begin by examining each variable by itself
(Chapter 1).
Then look at relationships between variables
(Chapter 2).
•
Begin by visualizing important features with graphs.
•
Then focus on speciﬁcs by using numerical summaries.
•
What graphics and numerical summaries are available for
relationships between variables?
Chapter 2
2
Relationships
•
To study a relationship between two variables, we
measure both variables on the same individuals.
•
We want to understand how a change in one
variable corresponds to a change in another
variable.
•
Since there will always be variability across
individuals, we are interested in overall
tendencies, understanding that there will be
individual exceptions.
Chapter 2
3
TwoVariable Relationships
What two variables are being examined?
•
Is there a gender gap in the preference of
candidates for governor of Iowa (Jim Nussle or
Chet Culver)?
•
Is there a difference in the distribution of annual
salaries for different levels of education (High
School, Bachelor’s, Professional Degree)?
Chapter 2
4
TwoVariable Relationships
What two variables are being examined?
•
How does tumor growth in laboratory animals
change as the dose of a drug increases?
•
Does the time required to complete a computer
programming task change based on the number
of years of experience of the programmer?
Chapter 2
5
Variable Types
•
From the examples, we can see that relationships
can involve any combination of categorical and
quantitative variables.
•
It is often natural to view one variable as having
an effect on, explaining, or inﬂuencing the other
variable.
•
This is especially true when we
control
the value
of one variable.
•
We can decide what dose of drug to give to laboratory animals.
Chapter 2
6
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View Full DocumentVariable Types
•
A
response variable
measures an outcome or a
result of a study.
•
Another name is a
dependent variable
.
•
The variable in a onevariable study is a response variable.
•
It may be a variable that we wish to
predict
.
•
An
explanatory variable
is a variable that
explains or inﬂuences a response variable.
•
Another name is a
independent variable
.
•
This is the variable that we could have control over.
Chapter 2
7
Explanatory and Response Variables
What are the explanatory and response variables?
•
Is there a gender gap in the preference of
candidates for governor of Iowa (Jim Nussle or
Chet Culver)?
•
Is there a difference in the distribution of annual
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 Spring '08
 ABBEY
 Computer Programming, programming task

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