The Experimental
Method in Psychology
Explaining Behaviour
Psychology 11
Scientific Method
O In order to EXPLAIN behaviour, psychologists
conduct carefully controlled experiments using
the SCIENTIFIC METHOD.
O We have already seen how psychologists gather
information (observations, case studies, and
surveys) in order to make predictions
(correlations between variables). Information
gathered is then put into carefully controlled
scientific testing using the EXPERIMENTAL
METHOD.
Experimental Method
1. Experiments start with OBSERVATION.
2. Based on their observations, psychologists
develop a SPECIFIC & TESTABLE HYPOTHESIS.
O Example: drinking alcohol negatively affects
memory.
Experimental Method
3. Now, to see if this hypothesis is true, we need to
MANIPULATE one variable. This variable is called the
INDEPENDENT VARIABLE. We are interested in studying
the EFFECT that this one variable has.
O What would the independent variable be in the above
example? We want to know if WHAT has an effect.
4. Yes, because we want to know if alcohol has an effect
on thinking, it will be the INDEPENDENT VARIABLE (the
variable that we manipulate). Therefore, we will expose one
group of subjects to the INDEPENDENT VARIABLE (the
alcohol).
Experimental Method
5. The group who is exposed to the
independent variable (sometimes
referred to as the TREATMENT) is
called the EXPERIMENTAL GROUP.
Experimental Method
6. However, in order to be sure that it is the alcohol
(and not something else) that had the effect, we
need a comparison group. This group is called the
CONTROL GROUP. The control group will be
exposed to everything that the subjects in the
experimental group are exposed to EXCEPT the
independent variable (the alcohol). So, if the
thinking abilities are different between the two
groups then we KNOW that it must be due to the
alcohol because the alcohol was the only
difference between the two groups.
Experimental Method
7. How do we ensure that the
EXPERIMENTAL GROUP and the
CONTROL GROUP are exactly the
same in every way other than the
independent variable (the
alcohol)?
Experimental Method
8. This is where a procedure called RANDOM
ASSIGNMENT comes in. By assigning your
subjects to groups randomly, the people in each
group should equal each other on things like their
age, their values, their opinions and on any other
characteristics. The idea behind random
assignment is that any person in your study could
just have easily ended up in the experimental
group as in the control group. Before the
experiment begins, both groups are equally similar.
So, you would need to use a random numbering
system to assign subjects to groups.
Experimental Method
9. In studies involving some kind of treatment
(taking a pill for example), researchers often use a
PLACEBO to make sure that both the experimental
and control group are similar. In this example, a
PLACEBO would involve giving the control groups
something that looks and tastes like alcohol, but
actually does not have any alcohol in it. This would
allow subjects in both groups to go through the
exact same experience during the experiment.
O Can you think of potential problems in this study,
if we did not use a PLACEBO?
Experimental Method
10. Another procedure that is used in
experiments to eliminate bias is called
DOUBLE-BLIND PROCEDURE. This
simply means that neither the
researcher who is conducting the study
nor the subjects in the study know who
is in the experimental group and who is
in the control group.
Experimental Method
11. Once we have ensured that both the
experimental group and control group are
equal on all variables except the
INDEPENDENT VARIBALE (the alcohol), then
we begin our study. Each group of subjects will
either receive alcohol (EXPERIMENTAL GROUP)
or receive an inert drink that looks and tastes
like alcohol, called a PLACEBO (CONTROL
GROUP).
Experimental Method
12. To see if alcohol had an effect on thinking,
we would give both groups a memory test. This
is called measuring to see if the
INDEPENDENT VARIABLE (the alcohol) had an
effect on the DEPENDENT VARIABLE.
O What is the dependent variable? What are we
measuring to see whether alcohol had an
effect?
Experimental Method
13. Yes, the memory test is the DEPENDENT
VARIABLE. The memory test will tell us if our
independent variable (the alcohol) had an effect
on our subject’s thinking ability.
14. Now you will simply calculate the results of the
memory test. If there is a difference between the
memory scores of the subject’s in the
experimental group and the memory of the
subject’s in the control group, you can assume that
it was due to the effect of the independent variable
– the alcohol.