Information Technology Reference
In-Depth Information
Figure 15.4
The data file for our numerical example.
15.4.2 STRUCTURING THE DATA ANALYSIS
From the main SPSS menu select
Analyze
General Linear Model
➜
Repeated Measures
.Youselected
Repeated Measures
for the following
reason. If there are two or more cases in the study and at least one of the
independent variables is a within-subjects variable, then we must partition
the total variance of the dependent variable into a between-subjects por-
tion and a within-subjects portion. This partitioning is accomplished by
the
Repeated Measures
module of the
General Linear Model
procedure
in SPSS.
Selecting this path will open the dialog window shown in Figure 15.5.
As you will recall from Chapters 12-14, this is the initial window used
by SPSS to have you name the within-subjects variable(s) in the study.
Therearetwosuchfactorsinourexample:
color
and
toytype
.Inthedata
file (as noted in section 15.4.1), reading the columns from left to right,
color
increments most slowly and
toytype
increments most rapidly. We
will use this information in identifying the within-subjects factors in
the
Repeated Measures Define Factor(s)
window. That is, we will first
identify the slowest incrementing variable,
color
in this case, and we will
then identify the more quickly incrementing variable,
toytype
in this case.
The results of this are shown in Figure 15.5.
Clicking
Define
in the
Define Factor(s)
window brings us to the main
dialog window of
GLM Repeated Measures
shown in Figure 15.6. There
are four slots that need to be specified in the panel to the right of the
variable list. With two levels for each of our two repeated measures, that
yields four variables; hence, our count of variables matches the number
of slots shown in the window (this is a very good thing).
➜
