Section 6: The Experiment:
Hunting for Causes
PSYCHOLOGY CHAPTER 1
 Experiment-
allows the researcher to
control or manipulate the situation
being studied
Allows the experimenter to draw
conclusions about cause & effect
 Must
adhere to ethical guidelines
In college, a review committee must
approve all proposed studies
Participants must volunteer & know
enough about the study to make an
intelligent decision (informed consent)
Must protect the participants from
physical or mental discomfort or harm
Also applies to animals
EXPERIMENTAL VARIABLES
Independent Variable:
A variable that an
experimenter
manipulates
 Dependent Variable:
A variable than an
experimenter predicts
will be affected by
manipulations of the
independent variable

 Every
experiment has at least one IV &
one DV
 Ideally everything in the experimental
situation except the IV is held constant
(same for all participants)
 Ensures that whatever happens is due
to the researchers manipulations &
nothing else
EXPERIMENTAL & CONTROL CONDITIONS
 Experiments
usually require both an
experimental & control condition
Experimental Condition: A condition in
which subjects are exposed to
manipulations of the IV
Control Condition: A comparison
condition in which subjects are not
exposed to the same treatment as in the
experimental condition
 Without
a control condition you can’t
be sure that the behavior you are
interested in would not have occurred
anyway without manipulation
EXPERIMENTAL DESIGN
 Hypothesis:
Nicotine in
cigarettes impairs
driving.
 All conditions kept the
same for both groups
except nicotine.
 Control condition is
given placebo
(inactive) cigarettes
 Number of collisions is
measured
1-8
 Use
random assignment to balance
individual characteristics
A procedure for assigning people to
experimental and control groups in
which individuals have the same
probability as an other of being
assigned to either group
 May
use placebos
An inactive substance
or fake treatment
used as a control in
an experiment or
given by a practitioner
to a patient.
Critical when testing
new drugs
EXPERIMENTER EFFECTS
 Because
expectations can influence the
results of a study, participants should
not know if they are in the experiment or
control groups
Single blind study
 Researchers
also bring expectations &
may cause unintended changes in
subjects’ behavior due to cues
inadvertently given by the experimenter
Facial expressions, posture, tone of
voice, or some other clue
 One
solution to this problem is to do a
double blind study
Experiment where neither subjects
nor people running the study know
which subjects are in the control
group and which are in the
experimental group until after results
are tallied
Standard in drug research
ADVANTAGES & LIMITATIONS OF EXPERIMENTS
 Experiments
allow conclusions about
cause-effect relationships.
 Participants in experiments are not
always representative of larger
population.
Much psychology research is carried
out using college students as
participants.
 Researcher
determines which
questions are asked & which
behaviors are recorded & the
participants try to do what they are
told
May act different than normal
 Dilemma-
the more control they exercise
over the situation, the more unlike real
life it may be
Do more field research
 Descriptive or experimental
research conducted in a natural
setting outside the laboratory