1. Examining Relationships
Chapter 3

2. Response Variable
Measures an outcome of a study
Dependent

3. Explanatory Variable Attempts to explain the observed outcomes
Independent

4. Scatterplots
Section 3.1

5. Scatterplot
Most effective way to display the relation between two quantitative variables measure on the same individuals.

6. Explanatory variable plotted on the x-axis
Response variable plotted on the y-axis
Categorical variables require different symbols.

7. Examining a Scatterplot
Look for an overall pattern and deviations from that pattern
Describe the pattern by the form, direction, and strength of the relationship

8. Positive association
One variable increases so does the other variable.
One variable decreases so does the other variable.
Similar to positive slope.

9. Negative association
One variable increases and the other variable decreases, or vice versa.
Similar to negative slope.

10. Correlation
Section 3.2

11. Measures the direction and strength of the linear relationship between two quantitative variables
Usually written as r

12. Facts About Correlation
Makes no distinction between explanatory and response variables
Requires both variables to be quantitative
Has no unit of measure…is just a number

13. Correlation is always between -1 and 1
Correlation only measures the strength of linear relationships
Correlation is not resistant
Correlation is not a complete description of two-variable data—always give mean and standard deviation as well

14. Practice Problems pg. 122 #3.1-3.4 pg. 135 #3.15-3.23