1. Warm-Up 4 minutes Graph each point in the same coordinate plane.
2) B(3,300)
3) C(6,150)
4) D(8,50)
5) Suppose that a line were drawn to connect the four points. Would its slope be positive or negative?

2. 1.5 Scatter Plots and Least-Squares Lines
Objectives:
Create a scatter plot and draw an informal inference about any correlation between the variables
Use a graphics calculator to find an equation for the least-squares line and use it to make predictions or estimates

3. Scatter Plot
A Scatter Plot is a set of coordinates (points) graphed on the same coordinate plane.
We can use scatter plots in order to look for patterns to help us make predictions in the future or past.

4. Chicken Pox in the United States
Scatter Plot
Chicken Pox in the U.S.
Year
Reported Cases
(in thousands)
1989
185.4
1990
173.1
1991
147.1
1992
158.4
1993
134.7
1994
151.2
Chicken Pox in the United States
Reported cases (1000’s) x y 20 40 60 80
100
120
140
160
180 1 2 3 4 5 6
# of years after 1988

5. no reliable correlation
negative correlation
no reliable correlation
positive correlation x y x y x y

6. Correlation and Prediction
no reliable correlation
perfect positive correlation
perfect negative correlation x y x y x y
r = -1
r = 0
r = 1

7. Least-Squares Line
(line that best fits the data) 2 4 6 8 10

8. Line of Best Fit on Calculator
Step 1: Press STAT select EDIT
Step 2: Type in values for List 1 and List 2
Step 3: Press STAT select CALC then select LinReg(ax + b) and press Enter.
Step 4: Write equation for line of best fit by substituting a and b.
STAT, EDIT, L1, L2, STAT, CALC, LinReg (ax + b)

9. Example 1
Create a scatter plot for the data shown below. Describe the correlation. Then find and graph an equation for the least-squares line. x 2 3 6 7 9 12 y 14 19 22 26 32 38

10. Example 2
The table below shows the number of juniors enrolled in Algebra 2 at LHS in six of the last 7 years. The number for the third year has been misplaced. Estimate the number of students enrolled in Algebra 2 in the third year.
year 1 2 4 5 6 7 # 33 29 45 43 61

11. Work with your group to make a prediction for the height at:
Age (months)
Height (inches) 18
76.1 19 77 20
78.1 21 22
78.8 23
79.7 24
79.9 25
81.1 26
81.2 27
82.8 28 29
83.5
Work with your group to make a prediction for the height at:
• 21 months
• 28 months
• 20 years

12. Homework