Quantitative assessment of the strength of the
relationship between x & y.
It is the measure of the extent to which x & y
are linearly related.
*It is strong if the points lie close to a straight
lint and is weak if they are widely scattered
about a line.
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

It’s a number between -1 and 1.
The closer it is to the ends, the stronger the
positive or negative relationship.
It gives the strength and direction.
Strong
Negative
-1
No
Correlation
Strong
Positive
0
1

www.whfreeman.com/tps4e
Think about z-scores of the x & y
Think about z-scores of the x & y
Think about z-scores of the x & y
r=
1
𝑛−1
𝑥−𝑥
𝑠𝑥
𝑦−𝑦
𝑠𝑦
=
𝑧𝑥 𝑧𝑦
𝑛−1
x
y
6
5
10
3
14
7
19
8
21
12
x
y
15
219
27
189
31
195
42
173
88
121
92
138
66
152
51
140
If you are asked to interpret a
correlation start by looking at a
scatterplot of the data. Then be
sure to address direction, form,
strength, and outliers and put your
answer in context.



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It does not depend on the unit of
measurement.
It doesn’t depend upon which of the 2
variables is “x”
It’s between -1 and 1
It equals -1 or 1 if all points lie on a straight
line
It is strongly affected by a few outliers
Scatterplots show
relationships – not
cause and effect.



Create scatterplot
Find the
correlation
Describe the
association
Fat (g) Sodium
29
920
31
1150
34
1200
35
1095
39
1180
39
1120
43
1260

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