Understanding Psychology (10th Ed)

correlation coeffi cient
A numerical 
measure that indicates the extent of the 
relationship between two variables.
FIGURE 1 
These scatterplots show relationships of diff erent strengths. In (a) and (b), the 
relationships are positive, although in (a) the relationship is considerably stronger than in 
(b). In contrast, the relationships in (c) and (d) are negative, with (d) representing a stronger 
negative relationship. Finally, (e) illustrates a case where no systematic relationship exists 
between the variables.
6 
0 
0 2 
(a) 
Strong positive relationship
(correlation = +.90)
(b) 
Moderate positive relationship
(correlation = +.60)
4 6 
1 3 5 
1 
2 
3 
4 
5 
6 
0 
0 2 4 6 
1 3 5 
1 
2 
3 
4 
5 
6 
0 
0 2 
(c) 
Moderate negative relationship
(correlation = –.50)
(d) 
Strong negative relationship
(correlation = –.90)
(e) 
No relationship
(correlation = .00)
4 6 
1 3 5 
1 
2 
3 
4 
5 
6 
0 
0 2 4 6 
1 3 5 
1 
2 
3 
4 
5 
6 
0 
0 2 4 6 
1 3 5 
1 
2 
3 
4 
5 
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 Module 
58 
Using Statistics to Answer Questions: Inferential Statistics and Correlation 
A-17
FIGURE 2 
In this distribution, each mother’s IQ score is compared to her daughter’s IQ score. 
Using a correlation coeffi
cient, we can calculate the strength of the relationship between the 
set of pairs of scores.