Of all of the methods presented, the
experimental method is the one that gives a researcher the most confidence when
making the decision to accept or reject a hypothesis. The experimental method
is a research tool characterized by a control over variables, the
identification of a cause (or causes), and a welldefined measure of behavior.
These aspects of the experimental method give it great power.
Four key concepts will help you
understand the experimental method: (1) the control group, (2) the experimental
group, (3) the independent variable, and (4) the dependent variable.
Definitions will be presented followed by an example incorporating all four
concepts into an experiment. The control group receives no treatment; it is
dealt with in a more or less conventional manner. It provides a standard of
comparison, a set of observations that can be contrasted with the behavior of
the experimental group.
The experimental group receives a novel
treatment, a condition (or set of conditions) that is presumed to affect
behavior. It is the target group, the one that will perhaps provide original or
particularly interesting data.
The independent
variable is one that is assigned to the subjects by the experimenter. There
will be at least two values, or measures, of this variable. It is the variable
that is thought of as a cause of behavior.
The dependent variable is a measure of
the behavior of the subjects. In most experiments, this variable can be
expressed as a set of scores. The dependent variable is associated with the effect
of a cause. Scores make it possible to compute statistical measures and make
evaluations based on the data. You will recall that near the beginning
of this chapter a teacher named Nora was said to have formed the hypothesis
that room temperature has an effect on test performance. Let‘s say that Nora
wants to do an experiment to evaluate this hypothesis.
Nora writes the names of sixty students
on a set of cards. The cards are shuffled and then dealt into two groups, Group
A and Group B. A coin is flipped. She says in advance that if heads comes up,
Group A will be the control group. If tails comes up, Group B will be the
control group. Heads comes up, and Group A becomes the control group. By
default, Group B is designated the experimental group.
It is important to note that the process
by which subjects are assigned to groups is a random process, meaning all
subjects have an equal chance of being included in either group. The aim of
this procedure is to cancel out the effects of individual differences in the
subjects that may have an effect on the experiment. Such variables as age, sex,
weight, intelligence, and income level are not, for the moment, under study. A
practical way to minimize the effects of such variables is to assign subjects
randomly to conditions.
The independent variable will be room
temperature. Let‘s say that most of the time Nora‘s students take tests in a
room that is 68 degrees Fahrenheit. The control group will be tested in a room
at this temperature. Up until now Nora has been thinking that
a ―cool room will have a positive effect on test performance. The time has
come to define ―cool more precisely. An operational definition is required, a
definition of a variable such as ―cool in terms of its
measurement operations. Nora decides that her operational definition of ―cool
will be a temperature of 55 degrees Fahrenheit. The word cool is an
imprecise, subjective term. On the other hand, 55 degrees Fahrenheit is precise
and objective. The experimental group will be tested at this temperature.
Let‘s say that subjects in both groups
are given the same twenty-question multiple-choice test. Scores range from a
low of 5 to a high of 20 correct. The mean (i.e., average) score for subjects
in the control group is 11. The mean score for subjects in the experimental
group is 14. On the surface, it appears that Nora will make the decision to
accept her experimental hypothesis. It appears that a cool room does in fact facilitate
test performance. Before a firm decision can be made to
accept or reject a hypothesis, a statistical evaluation of the data must be
made. A difference between means is sometimes due to chance.
An experiment can, of course, be much
more interesting than the one described, and there can be two or more
independent variables. However, Nora‘s experiment was presented because it
reveals the essentials of the experimental method.
(Sumber: Catatan dari Bacaan English for Psychology of Student)
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