Statistics for the Behavioral Sciences by Frederick J. Gravetter, Larry B. Wallnau ISBN 10: 1305504917 ISBN 13: 9781305504912

SECTION 1.2 | Data Structures, Research Methods, and Statistics 15
for controlling variables is to use matching to ensure equivalent groups or equivalent environments.
For example, the researcher could match groups by ensuring that every group
has exactly 60% females and 40% males. Finally, the researcher can control variables by
holding them constant. For example, in the video game violence study discussed earlier
(Polman et al., 2008), the researchers used only 10-year-old boys as participants (holding
age and gender constant). In this case the researchers can be certain that one group is not
noticeably older or has a larger proportion of females than the other.
DEFINITION
In the experimental method, one variable is manipulated while another variable
is observed and measured. To establish a cause-and-effect relationship between the
two variables, an experiment attempts to control all other variables to prevent them
from influencing the results.
■ Terminology in the Experimental Method
Specific names are used for the two variables that are studied by the experimental method. The
variable that is manipulated by the experimenter is called the independent variable. It can be
identified as the treatment conditions to which participants are assigned. For the example in
Figure 1.5, the amount of violence in the video game is the independent variable. The variable
that is observed and measured to obtain scores within each condition is the dependent variable.
For the example in Figure 1.5, the level of aggressive behavior is the dependent variable.
DEFINITION
The independent variable is the variable that is manipulated by the researcher. In
behavioral research, the independent variable usually consists of the two (or more) treatment
conditions to which subjects are exposed. The independent variable consists of the
antecedent conditions that were manipulated prior to observing the dependent variable.
The dependent variable is the one that is observed to assess the effect of the treatment.
Control Conditions in an Experiment An experimental study evaluates the relationship
between two variables by manipulating one variable (the independent variable) and
measuring one variable (the dependent variable). Note that in an experiment only one
variable is actually measured. You should realize that this is different from a correlational
study, in which both variables are measured and the data consist of two separate scores
for each individual.
Often an experiment will include a condition in which the participants do not receive
any treatment. The scores from these individuals are then compared with scores from participants
who do receive the treatment. The goal of this type of study is to demonstrate that
the treatment has an effect by showing that the scores in the treatment condition are substantially
different from the scores in the no-treatment condition. In this kind of research,
the no-treatment condition is called the control condition, and the treatment condition is
called the experimental condition.
DEFINITION
Individuals in a control condition do not receive the experimental treatment.
Instead, they either receive no treatment or they receive a neutral, placebo treatment.
The purpose of a control condition is to provide a baseline for comparison
with the experimental condition.
Individuals in the experimental condition do receive the experimental treatment.