1. Chapter 4 Scatterplots – Descriptions

2. Scatterplots Graphical display of two quantitative variables We plot the explanatory (independent) variable on the x-axis and the response (dependent) variable on the y-axis Each dot represents a single observation and it’s two values Categorical variables may be included by adding in different colors or symbols

3. Determine Explanatory and Response Variables Hours of studying & grade on a test # of tumors the mice develop & # of grams of a toxin given to lab mice Yearly income & life expectancy

4. Describing Scatterplots 4 things that must be talked about: ◦ Direction ◦ Form ◦ Strength ◦ Unusual elements

5. Direction Positive: as values of the explanatory variable increase, values in the response variable tend to increase

6. Direction Negative: as values of the explanatory variable increase, value in the response variable tend to decrease

7. Direction None: no discernable change in the response variable

8. Form (Shape) Linear: The shape has the appearance of a linear relationship. Does not have to fit it perfectly.

9. Form Curved

10. Form None No discernable form

11. Strength (Scatter) Strong association: very little scatter

12. Strength Moderate strength:

13. Strength Weak strength: lots of scatter

14. Unusual Features Outliers

15. Practice Negative Curved Moderately Strong No outliers

16. Positive Linear Weak No outliers

17. Positive Linear Moderately strong Possible outlier around (9, 35).

18. No direction No form No apparent association Possible outlier around (60,8).

19. Positive Curved Strength weakens as the explanatory variable increases No outliers