1. EXAMPLE 1
Describe correlation
Telephones
Describe the correlation shown by each scatter plot.

2. EXAMPLE 1
Describe correlation
SOLUTION
The first scatter plot shows a positive correlation, because as the number of cellular phone subscribers increased, the number of cellular service regions tended to increase.
The second scatter plot shows a negative correlation, because as the number of cellular phone subscribers increased, corded phone sales tended to decrease.

3. EXAMPLE 2
Estimate correlation coefficients
Tell whether the correlation coefficient for the data is
closest to – 1, – 0.5, 0, 0.5, or 1. a.
SOLUTION
a. The scatter plot shows a clear but fairly weak negative
correlation. So, r is between 0 and – 1, but not too close
to either one. The best estimate given is r = – 0.5.
(The actual value is r –0.46.)

4. EXAMPLE 2
Estimate correlation coefficients b.
SOLUTION
b. The scatter plot shows approximately no correlation.
So, the best estimate given is r = 0.
(The actual value is r – 0.02.)

5. EXAMPLE 2
Estimate correlation coefficients c.
SOLUTION
c. The scatter plot shows a strong positive correlation.
So, the best estimate given is r = 1.
(The actual value is r )

6. GUIDED PRACTICE
for Examples 1 and 2
For each scatter plot, (a) tell whether the data have a positive correlation, a negative correlation, or approximately no correlation, and (b) tell whether the correlation coefficient is closest to –1, – 0.5, 0, 0.5, or 1. 1.
ANSWER
(a) positive correlation
(b) r = 0.5

7. GUIDED PRACTICE
for Examples 1 and 2
For each scatter plot, (a) tell whether the data have a positive correlation, a negative correlation, or approximately no correlation, and (b) tell whether the correlation coefficient is closest to –1, – 0.5, 0, 0.5, or 1. 2.
ANSWER
(a) negative correlation
(b) r = –1

8. GUIDED PRACTICE
for Examples 1 and 2
For each scatter plot, (a) tell whether the data have a positive correlation, a negative correlation, or approximately no correlation, and (b) tell whether the correlation coefficient is closest to –1, –0.5, 0, 0.5, or 1. 3.
ANSWER
(a) no correlation
(b) r = 0