1. Scatterplots and Correlation
BPS 7e Chapter 4
© 2014 W. H. Freeman and Company

2. Explanatory and Response
A researcher wants to know if taking increasing amounts of ginkgo biloba will result in increased memory capacity 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?
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

3. Explanatory and Response (answer)
A researcher wants to know if taking increasing amounts of ginkgo biloba will result in increased memory capacity 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?
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

4. Explanatory and Response
A study examines if state political repression increases the chances for popular revolution. What is the response variable in this study?
state
popular revolution
state political repression
repression

5. Explanatory and Response (answer)
A study examines if state political repression increases the chances for popular revolution. What is the response variable in this study?
state
popular revolution
state political repression
repression

6. Displaying Relationships
If a data set consists of two variables measured on each of 20 individuals, how many dots are in the scatterplot? 10 20 30 40

7. Displaying Relationships (answer)
If a data set consists of two variables measured on each of 20 individuals, how many dots are in the scatterplot? 10 20 30 40

8. Displaying Relationships
Everyone will draw the same conclusions about form, direction, and strength from a scatterplot.
True
False

9. Displaying Relationships (answer)
Everyone will draw the same conclusions about form, direction, and strength from a scatterplot.
True
False

10. Interpreting Scatterplots
Look at the following scatterplot. Choose which description BEST fits the plot.
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

11. Interpreting Scatterplots (answer)
Look at the following scatterplot. Choose which description BEST fits the plot.
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

12. Interpreting Scatterplots
Look at the following scatterplot. Choose which description BEST fits the plot.
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

13. Interpreting Scatterplots (answer)
Look at the following scatterplot. Choose which description BEST fits the plot.
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

14. Interpreting Scatterplots
Look at the following scatterplot. Choose which description BEST fits the plot.
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

15. Interpreting Scatterplots (answer)
Look at the following scatterplot. Choose which description BEST fits the plot.
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

16. Interpreting Scatterplots
Which of the following scatterplots displays the stronger linear relationship?
Plot A
Plot B
Same for both

17. Interpreting Scatterplots (answer)
Which of the following scatterplots displays the stronger linear relationship?
Plot A
Plot B
Same for both

18. Interpreting Scatterplots
Which phrase best describes the strength of this relationship?
very weak
moderate
mod. strong
strong

19. Interpreting Scatterplots (answer)
Which phrase best describes the strength of this relationship?
very weak
moderate
mod. strong
strong

20. Adding Categorical Variables
Look at the following scatterplot. Which variable is categorical?
Height
Weight
Gender

21. Adding Categorical Variables (answer)
Look at the following scatterplot. Which variable is categorical?
Height
Weight
Gender

22. Adding Categorical Variables
What do we learn by using different symbols for men and women in the
following scatterplot of
shoe size versus
height?
The form is positive.
The form is linear.
The relationship is moderately strong.
Six or seven men likely didn’t record their height correctly.

23. Adding Categorical Variables (answer)
What do we learn by using different symbols for men and women in the
following scatterplot of
shoe size versus
height?
The form is positive.
The form is linear.
The relationship is moderately strong.
Six or seven men likely didn’t record their height correctly.

24. Correlation
For which of the following situations would it be appropriate to calculate r, the correlation coefficient?
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

25. Correlation (answer)
For which of the following situations would it be appropriate to calculate r, the correlation coefficient?
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

26. Correlation
What is a FALSE statement about r, the correlation coefficient?
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.

27. Correlation (answer)
What is a FALSE statement about r, the correlation coefficient?
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.

28. Correlation Which scatterplot would give a larger value for r? Plot A
Plot B
It would be the same for both plots. y y x x

29. Correlation (answer)
Which scatterplot would give a larger value for r?
Plot A
Plot B
It would be the same for both plots. y y x x

30. Correlation
Which of the following is the correlation of understanding (of biology) with attitude for the following scatterplot?
–0.75
–0.04
0.63
0.98

31. Correlation (answer)
Which of the following is the correlation of understanding (of biology) with attitude for the following scatterplot?
–0.75
–0.04
0.63
0.98

32. Facts about 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.
True
False y x

33. Facts about 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.
True
False y x

34. Facts about Correlation
Compare the correlation coefficient, r, for the data in Plots A and B.
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. y y x x

35. Facts about Correlation (answer)
Compare the correlation coefficient, r, for the data in Plots A and B.
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. y y x x

36. Facts about Correlation
If we change the height measure (X) from inches into centimeters and weight measure (Y) from pounds into kilograms, what will happen to the correlation (r) coefficient?
Correlation will increase.
Correlation will decrease.
Correlation will remain the same.

37. Facts about Correlation (answer)
If we change the height measure (X) from inches into centimeters and weight measure (Y) from pounds into kilograms, what will happen to the correlation (r) coefficient?
Correlation will increase.
Correlation will decrease.
Correlation will remain the same.

38. Facts about Correlation
Given that the correlation between MPG (miles per gallon) and a car’s weight is –0.85; when reversed, the correlation between a car’s weight and MPG should become
True
False

39. Facts about Correlation (answer)
Given that the correlation between MPG (miles per gallon) and a car’s weight is –0.85; when reversed, the correlation between a car’s weight and MPG should become
True
False