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conditions,
or
treatment effects
. In our example, the color of the room in
which participants completed the mood inventory was the independent
variable. The room color was either blue or red; these are said to be the
values
or
levels
of the independent variable. Although room color took on
only two possible values in this study, such variation is enough to define it
as a variable. It is conceived as an independent variable because it would
be the presumed cause of differences in mood scores between the groups.
1.3.4 THE RELATIONSHIP OF DEPENDENT AND
INDEPENDENT VARIABLES
Dependent and independent variables are intimately related to each other.
Dependent variables are presumed to be influenced or affected by inde-
pendent variables. In the example, the dependent variable of mood was
thought to be influenced by the color of the room in which the students
answered the mood questions. The form that this influence takes is a
function of the nature of the research. In the example, the influence is
presumed to be causative; that is, the possibility that room color caused
or produced differences in mood was examined.
Another way to express the idea of influence is to predict the depen-
dent variable based on the values of the independent variable. For example,
we might want to predict the degree to which individuals hold intrinsi-
cally motivated goals such as making contributions to their community
and having enriched relationships with other people. This could be mea-
sured by a paper-and-pencil inventory. Using a nonexperimental research
design, we could administer other inventories such as those measuring
self-esteem and spirituality. These latter two variables could then be used
to predict the degree of intrinsic motivation reported by participants. In
doing so, these predictors would be treated as independent variables in
the data analysis.
1.4 THE IMPORTANCE OF VARIATION
The key element to bear in mind when we talk about dependent variables
and independent variables is that in order to be a viable variable in our
statistical analysis, that variable must demonstrate variation in our study;
if it does not vary, it is a constant rather than a variable. Although this may
sound obvious, remembering this maxim can be quite helpful in selecting
variables for a research design and in designing a research study.
In terms of independent variables, this requirement of variation is
really an absolute rule. In our example study, if all of the participants
completed the mood inventory in the same color room, then room color
would not be able to be used as an independent variable in our study.
Yes, room color in the abstract is a variable in that rooms can take on a
wide variety of values (colors), but in the specific circumstances of our
experiment, in order for room color to be a variable, we must make sure
that it varies for the two groups in question.
