1. Scatterplots and Correlations

2. Scatterplots
Describing relationship on bivariate data

3. Scatterplots and Correlation

4. 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?
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.

5. 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?
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.

6. Numeric bivariate data
The first step in analyzing numeric bivariate data is to
Measure strength of linear relationship.
Create a scatterplot.
Model linear relationship with regression line.

7. Numeric bivariate data (answer)
The first step in analyzing numeric bivariate data is to
Measure strength of linear relationship.
Create a scatterplot.
Model linear relationship with regression line.

8. 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

9. 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

10. 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

11. 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

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

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

16. Scatterplots
Look at the following scatterplot. Which variable is categorical?
Height
Weight
Gender

17. Scatterplots (answer)
Look at the following scatterplot. Which variable is categorical?
Height
Weight
Gender

18. tips for drawing scatterplots
1. SCALE THE HORIZONTAL AND VERTICAL AXES. INTERVAL MUST BE UNIFORM (DISTANCE OF THE TICK MARKS). IF THE SCALE DOES NOT BEGIN AT ZERO, INDICATE A BREAK ON YOUR PLOT.
2. LABEL BOTH AXES
3. IF YOU ARE GIVEN A GRID, TRY TO ADOPT A SCALE SO THAT YOUR PLOT USES THE WHOLE GRID. DON’T COMPRESS THE PLOT INTO ONE CORNER OF THE GRID.

19. “r” ranges from −1 to +1
“r” quantifies the strength and direction of a linear relationship between two quantitative variables.
Strength: How closely the points follow a straight line.
Direction is positive when individuals with higher x values tend to have higher values of y.

20. Categorical Variables in Scatterplots
TO ADD CATEGORICAL VARIABLE TO A SCATTERPLOT, USE A DIFFERENT COLOR OR SYMBOL FOR EACH CATEGORY.