Scatterplots and Correlation BPS chapter 4 © 2006 W.H. Freeman and Company

Scatterplots and Correlation
BPS chapter 4
© 2006 W.H. Freeman and Company
Explanatory variables
A researcher wants to know if taking increasing amounts of ginkgo
biloba will result in increased capacities of memory ability for
different students. He administers it to the students in doses of 250
milligrams, 500 milligrams, and 1000 milligrams. What is the
explanatory variable in this study?
a)
b)
c)
d)
Amount of ginkgo biloba given to each student.
Change in memory ability.
Size of the student’s brain.
Whether the student takes the ginkgo biloba.
Explanatory variables (answer)
A researcher wants to know if taking increasing amounts of ginkgo
biloba will result in increased capacities of memory ability for
different students. He administers it to the students in doses of 250
milligrams, 500 milligrams, and 1000 milligrams. What is the
explanatory variable in this study?
a)
b)
c)
d)
Amount of ginkgo biloba given to each student.
Change in memory ability.
Size of the student’s brain.
Whether the student takes the ginkgo biloba.
Numeric bivariate data
The first step in analyzing numeric bivariate data is to
a)
b)
c)
Measure strength of linear relationship.
Create a scatterplot.
Model linear relationship with regression line.
Numeric bivariate data (answer)
The first step in analyzing numeric bivariate data is to
a)
b)
c)
Measure strength of linear relationship.
Create a scatterplot.
Model linear relationship with regression line.
Scatterplots
Look at the following scatterplot. Choose which description BEST fits
the plot.
a)
b)
c)
d)
e)
Direction: positive, form: linear, strength: strong
Direction: negative, form: linear, strength: strong
Direction: positive, form: non-linear, strength: weak
Direction: negative, form: non-linear, strength: weak
No relationship
Scatterplots (answer)
Look at the following scatterplot. Choose which description BEST fits
the plot.
a)
b)
c)
d)
e)
Direction: positive, form: linear, strength: strong
Direction: negative, form: linear, strength: strong
Direction: positive, form: non-linear, strength: weak
Direction: negative, form: non-linear, strength: weak
No relationship
Scatterplots
Look at the following scatterplot. Choose which description BEST fits
the plot.
a)
b)
c)
d)
e)
Direction: positive, form: non-linear, strength: strong
Direction: negative, form: linear, strength: strong
Direction: positive, form: linear, strength: weak
Direction: positive, form: non-linear, strength: weak
No relationship
Scatterplots (answer)
Look at the following scatterplot. Choose which description BEST fits
the plot.
a)
b)
c)
d)
e)
Direction: positive, form: non-linear, strength: strong
Direction: negative, form: linear, strength: strong
Direction: positive, form: linear, strength: weak
Direction: positive, form: non-linear, strength: weak
No relationship
Scatterplots
Look at the following scatterplot. Choose which description BEST fits
the plot.
a)
b)
c)
d)
e)
Direction: positive, form: non-linear, strength: strong
Direction: negative, form: linear, strength: strong
Direction: positive, form: linear, strength: weak
Direction: positive, form: non-linear, strength: weak
No relationship
Scatterplots (answer)
Look at the following scatterplot. Choose which description BEST fits
the plot.
a)
b)
c)
d)
e)
Direction: positive, form: non-linear, strength: strong
Direction: negative, form: linear, strength: strong
Direction: positive, form: linear, strength: weak
Direction: positive, form: non-linear, strength: weak
No relationship
Scatterplots
Which of the following scatterplots displays the stronger linear
relationship?
a)
b)
c)
Plot A
Plot B
Same for both
Scatterplots (answer)
Which of the following scatterplots displays the stronger linear
relationship?
a)
b)
c)
Plot A
Plot B
Same for both
Scatterplots
Look at the following scatterplot. Which variable is categorical?
a)
b)
c)
Height
Weight
Gender
Scatterplots (answer)
Look at the following scatterplot. Which variable is categorical?
a)
b)
c)
Height
Weight
Gender
Correlation
For which of the following situations would it be appropriate to calculate
r, the correlation coefficient?
a)
b)
c)
d)
Time spent studying for statistics exam and score on the exam.
Income for county employees and their respective counties.
Eye color and hair color of selected participants.
Party affiliation of senators and their vote on presidential
impeachment.
Correlation (answer)
For which of the following situations would it be appropriate to calculate
r, the correlation coefficient?
a)
b)
c)
d)
Time spent studying for statistics exam and score on the exam.
Income for county employees and their respective counties.
Eye color and hair color of selected participants.
Party affiliation of senators and their vote on presidential
impeachment.
Correlation
What is a FALSE statement about r, the correlation coefficient?
a)
b)
c)
d)
It is a product of z-scores of X and Y.
It can range in value from –1 to 1.
It measures the strength and direction of the linear relationship
between X and Y.
It is measured in units of the X variable.
Correlation (answer)
What is a FALSE statement about r, the correlation coefficient?
a)
b)
c)
d)
It is a product of z-scores of X and Y.
It can range in value from –1 to 1.
It measures the strength and direction of the linear relationship
between X and Y.
It is measured in units of the X variable.
Correlation
Which scatterplot would give a larger value for r?
a)
b)
c)
Plot A
Plot B
It would be the same for both plots.
Correlation (answer)
Which scatterplot would give a larger value for r?
a)
b)
c)
Plot A
Plot B
It would be the same for both plots.
Correlation
True or False? Computing r as a measure of the strength of the
relationship between X and Y is appropriate for the data in the
following scatterplot:
a)
b)
True
False
Correlation (answer)
True or False? Computing r as a measure of the strength of the
relationship between X and Y is appropriate for the data in the
following scatterplot:
a)
b)
True
False
Correlation
Compare the correlation coefficient, r, for the data in Plots A and B.
a)
b)
c)
d)
r in Plot A is less than r in Plot B.
r in Plot A is equal to r in Plot B.
r in Plot A is greater than r in Plot B.
Not enough information exists to compare the two r’s.
Correlation (answer)
Compare the correlation coefficient, r, for the data in Plots A and B.
a)
b)
c)
d)
r in Plot A is less than r in Plot B.
r in Plot A is equal to r in Plot B.
r in Plot A is greater than r in Plot B.
Not enough information exists to compare the two r’s.