Understanding Psychology (10th Ed)

relationship:
As values of variable x increase, the values of variable y decrease. In 
(e), no clear relationship exists between variable x and variable y .
It is also possible to consider scores in terms of their mathematical relationship 
to one another rather than simply the way they appear on a scatterplot. Suppose, 
for example, a psychologist was interested in the degree to which a daughter’s IQ 
was related to her mother’s IQ—specifi cally, if a mother with a high IQ tended to 
have a daughter who also had a high IQ—and whether a mother with a low IQ 
tended to have a daughter with a low IQ. To examine the issue, suppose the psy-
chologist measured the IQs of 10 mothers and daughters and arranged their IQs as 
presented in Figure 2 on page A-17. 
Looking at the data in the table, it is obvious that mothers and daughters do 
not have identical IQs. Moreover, they do not even have IQs that are rank-ordered 
the same in the two columns. For example, the mother with the highest IQ does not 
have the daughter with the highest IQ, and the mother with the lowest IQ does not 
signifi cant outcome
An outcome in 
which the observed outcome would be 
expected to have occurred by chance 
with a probability of .05 or less.
positive relationship
A relationship 
established by data that shows high 
values of one variable corresponding 
with high values of another, and low 
values of the fi rst variable correspond-
ing with low values of the other.
negative relationship
A relationship 
established by data that shows high 
values of one variable corresponding 
with low values of the other.
feL82795_app_A2-A19.indd Page A-15 8/6/10 8:15 PM user-f465
feL82795_app_A2-A19.indd Page A-15 8/6/10 8:15 PM user-f465
/Users/user-f465/Desktop
/Users/user-f465/Desktop

---

A-16 Appendix 
Going by the Numbers: Statistics in Psychology
have the daughter with the lowest IQ. It is apparent, then, that there is not a perfect
relationship between the IQ of a mother and the IQ of a daughter. However, it 
would be a mistake to conclude that there is a zero, or no, relationship between the 
IQs of the mothers and daughters because it is clear that there is a tendency for 
mothers who have high IQs to have daughters with high IQs, and that mothers with 
low IQs tend to have daughters with low IQs. 
The statistic that provides a precise mathematical index of the degree to which 
two variables are related is the correlation coeffi cient. A correlation coeffi cient is a 
numerical measure that indicates the extent of the relationship between two vari-
ables. It ranges in value from 
1
1.00 to 
2
1.00. A value of 
1
1.00 would indicate that 
two variables had a perfect positive relationship with one another, which means that 
the highest score on one variable would be associated with the highest score on the 
other variable, the second-highest score on the fi rst variable would be associated with 
the second-highest score on the second variable, and so on. A value of 
2
1.00 would 
indicate that there was a perfect negative relationship between the two variables; the