1. Chapter 2 – Linear Equations and Functions
2.7 – Scatter Plots and Correlation

2. 2.7 – Scatter Plots and Correlation
In this section we will review:
Correlations in scatter plots and finding a best-fitting line

3. 2.7 – Scatter Plots and Correlation
Scatter plot – graph of a set of data pairs (x, y )
Can help identify the relationship, or correlation, between two variables

4. 2.7 – Scatter Plots and Correlation
Positive correlation
As x increases, y increases.

5. 2.7 – Scatter Plots and Correlation
Negative correlation
As x increases, y decreases

6. 2.7 – Scatter Plots and Correlation
Relatively no correlation
There is no obvious pattern between x and y

7. 2.7 – Scatter Plots and Correlation
Example 1
Describe the correlation shown by the scatter plot.

8. 2.7 – Scatter Plots and Correlation
Example 2
Describe the correlation shown in the scatter plot.

9. 2.7 – Scatter Plots and Correlation
Best-fitting line – the line that most closely models the data
When points lie close, almost forming a line with positive or negative slope, the correlation is strong.

10. 2.7 – Scatter Plots and Correlation
Approximating a Best-Fitting Line
Draw a scatter plot
Sketch a line that follows the trend. The line should be close to as many points as possible.
Choose two points that lie on the line and estimate the coordinates (they do NOT have to be original points)
Write an equation for the two points from step 3.

11. 2.7 – Scatter Plots and Correlation
Example 3
The table gives the systolic blood pressure y of patients x years old. Approximate the best-fitting line for the data.

12. 2.7 – Scatter Plots and Correlation
Example 4
These data represent purchases at five gas stations in a city.
Approximate the best-fitting line.
Predict the cost of 10 gallons of gasoline.

13. 2.7 – Scatter Plots and Correlation
HOMEWORK
Worksheet 2.7 Practice A