1. Prof. Eric A. Suess Chapter 3
Statistics 3502/6304
Prof. Eric A. Suess
Chapter 3

2. Data Description – Three or more Quantitative Variables
Correlation Matrix
Scatterplot Matrix

3. Two Quantitative Variables
When we have two quantitative variables X and Y then we can look at the association between the variables.
Scatterplots Figure 3.31 gives examples of what scatterplots look like for different correlation values. 0≤𝑟≤1
Correlation
𝑟= 1 𝑛−1 𝑖=1 𝑛 𝑥 𝑖 − 𝑥 𝑠 𝑥 𝑦 𝑖 − 𝑦 𝑠 𝑦

4. Data Description – Three or more Quantitative Variables
Correlation Matrix
If we have many variables we can compute the correlation for all pair of quantitative variables.
See Exercise AIDS, syphilis, tuberculosis

5. Correlation Matrix
Correlation: AIDS, Syphilis, Tuber. AIDS Syphilis Syphilis Tuber Cell Contents: Pearson correlation P-Value

6. Scatterplot Matrix

7. Scatterplot Matrix – Linear Regression

8. Scatterplot Matrix – Quadratic Linear Regression

9. Scatterplot Matrix – Cubic Linear Regression

10. Regression Models Linear 𝑦=𝑎+𝑏𝑥+𝜀 Quadratic 𝑦=𝑎+𝑏𝑥+𝑐𝑥²+𝜀 Cubic
𝑦=𝑎+𝑏𝑥+𝑐 𝑥 2 +𝑑𝑥³+𝜀
𝜀 is the error in the model