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TEKS
2.6
a.5, 2A.1.B
Draw Scatter Plots
and Best-Fitting Lines
Before You wrote equations of lines.
Key Vocabulary
• scatter plot
• positive correlation
• negative correlation
• correlation
coefficient
• best-fitting line
Now You will fit lines to data in scatter plots.
Why? So you can model sports trends, as in Ex. 27.
A scatter plot is a graph of a set of data pairs (x, y). If y tends to increase as x
increases, then the data have a positive correlation. If y tends to decrease as
x increases, then the data have a negative correlation. If the points show no
obvious pattern, then the data have approximately no correlation.
y
Positive
correlation
x
y
Negative
correlation
E XAMPLE 1 Describe correlation
x
2.6 Draw Scatter Plots and Best-Fitting Lines 113
y
Approximately
no correlation
TELEPHONES Describe the correlation shown by each scatter plot.
Cellular Phone Subscribers and
Cellular Service Regions,
1995–2003
Cellular service regions
(thousands)
y
160
120
80
40
Solution
0 0
40 80 120 160 x
Subscribers (millions)
Cellular Phone Subscribers and
Corded Phone Sales,
1995–2003
Corded phone sales
(millions of dollars)
y
550
450
350
250
0
40 80 120 160 x
Subscribers (millions)
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.
x