Information Technology Reference
In-Depth Information
Figure 16.7
We have selected
Regression
on the
Method
menu.
Make sure that the checkbox for
Include constant in equation
is checked.
Furthermore, because the linearity assumption is tested on the sam-
ple as a whole, we need to check
Total
under
Fit lines for
toward the
bottom of the window (this is the default). Click
OK
to perform the
analysis.
The resulting scatterplot is shown in Figure 16.8. As can be seen in
the figure, the relationship between the dependent variable of number of
math problems solved correctly and the covariate of verbal ability seems
to be linear. Hence, the assumption of linearity of regression appears to
have been met.
16.8.2 HOMOGENEITY OF REGRESSION
The assumption of homogeneity of regression maintains that the regres-
sion lines predicting the dependent variable from the covariate have com-
parable slopes across the groups. This is tested by obtaining a nonsignifi-
cant Groups
Covariate interaction effect.
From the main SPSS menu select
Analyze
×
General LinearModel
➜
Univariate.
Selecting this path will open the dialog window shown in
Figure 16.9. We have configured it with
group
as the fixed factor,
math_dv
as the dependent variable, and
verb_cov
as the covariate.
➜
