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Looking at data: relationships

Correlation
IPS chapter 2.2
Copyright Brigitte Baldi 2005 ©
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Correlation
The correlation coefficient “r”
R does not distinguish x and y
R has no units
R ranges from 1 to +1
Influential points
The correlation coefficient is a measure of the direction and strength of a
linear relationship between two quantitative variables x and y.
The correlation coefficient "r"
Student (i)
IQ score
(x)
Self
Concept
Score (y)
i=1
x
1
= 110
y
1
= 58
i=2
x
2
= 124
y
2
= 72
i=3
x
3
= 126
y
3
= 80
Correlation can only be used to
describe
quantitative
variables.
Categorical variables don’t have
means and standard deviations.
r?
of
value
the
is
What
14
.
11
s
,
70
72
.
8
s
,
120
y
x
=
=
=
=
y
x
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The correlation coefficient, r, treats
x and y symmetrically.
r = 0.75
r = ?
The correlation coefficient, r, treats
x and y symmetrically.
"Time to swim" is the explanatory variable here, and belongs on the x axis.
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This note was uploaded on 03/03/2009 for the course PAM 2100 taught by Professor Abdus,s. during the Fall '08 term at Cornell University (Engineering School).
 Fall '08
 ABDUS,S.

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