Chapter 8
Solving Problems: Controlling Extraneous
Variables
Physical Variables
Social Variables
Personality Variables
Context Variables
Physical Variables
are aspects of the testing situation that
need to be controlled:
day of the week
experimental room
lighting
Elimination
- completely removes extraneous physical variables from the experimental
situation (e.g., soundproofing a room)
- Removal of extraneous physical variables prevents them from operating
differently across different treatment conditions.
Constancy of Conditions
- controls extraneous physical variables by keeping all aspects of the treatment
conditions identical except for the independent variable.
Example: test all subjects in the same room or at the same time of the day.
How does
balancing work?
Balancing
- controls extraneous physical
variables by equally distributing their
effects across treatment conditions.
Example: running half of the
subjects in each condition in the
morning and half in the evening.
In which order should you use
these techniques?
1
2
3
Eliminate
Keep conditions
Balance the
extraneous
constant where
effects of
variables
elimination is not
extraneous
whenever
possible.
variables when
possible.
constancy of
conditions is not
possible.
Social Variables
are
aspects
of
the
relationships
between
subjects
and
experiments that can influence experimental results.
These
bias.
includes
demand
characteristics
and
experimenter
EAST
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Solution
Solving an equation as a class certainly boosts students’ interest and engagement.
Aside from helping them stay focused, it allows them to think deeply, create
connections, and get different perspectives on the subject matter.
Demand
Characteristics
- are cues within the experimental
situation that demand or elicit specific
participant responses.
Example: students cue professors to wrap
up their lectures by packing their binders,
books, and water bottle bottles and by
looking at the door.
How can demand characteristics
threaten internal validity?
Demand characteristics can confound an experiment
if they vary across experimental conditions.
Subjects may act to confirm what they think is the experimental hypothesis.
What is a single-blind
experiment?
In a single- blind experiment, subjects are not told
their treatment condition.
For example, in a single- blind drug study, the experimental
and control groups might receive capsules that look and taste
identical.
How do single-blind
experiments control demand
characteristics?
When subjects are not told their treatment condition, this
eliminates cues that might alter their behavior.
Placebo Effect
The placebo effect is when a
subject receives an inert treatment
and improves because of positive
experiences.
How do cover stories control
demand characteristics?
A cover story is a false plausible explanation of
the experimental procedures to disguise the
research hypothesis from the subjects.
They should be used sparingly, since they are a
form of deception.
Experimenter
Bias
- is any behavior by the experimenter
that can confound experiment.
For example, an experimenter might
provide more attention to subjects in
one condition than another.
Rosenthal Effect
-
This
is
the
phenomenon
in
which
experimenters subjects differently based
on their expectations and their resulting
actions influence subject performance.
- This is also called the Pygmalion effect
and self-fulfilling prophecy.
Example of Rosenthal
Effect
Teachers
might
give
more
attention
and
feedback to high aptitude students that to low
aptitude students.
The
Rosenthal
experiment,
effect
producing
can
results
confound
consistent
the experimenter's expectations.
an
with
Why is double-blind design superior to
a single-blind design in controlling
experimenter bias?
Single-blind experimenters
Double-blind experimenters
Only control demand
Control both demand
characteristics, since subjects are
characteristics and experimenter
blinded to theri condition.
bias, since both the experimenter
and subjects are blinded.
How might an experimenter's
personality affect experimental
results?
Research
on
experimenter
personality
shows
that
when
experimenters are warm and friendly, subjects learn more, talk
more, earn better test scores, and are eager to please.
Hostile or authoritarian experimenters obtain inferior subject
performace.
How can experimenters
control personality variables?
Employ multiple experimenters to run a equal
number of subjects in each of the experimental
conditions (balancing).
Treat "experimenter" as an independent variable in
statistical analysis. If an interaction is found, then
the experiment was confounded.
When there is a single experimenter, minimize face
to face contact and closely follow the script.
Videotape sessions to confirm consistent
performance.
How do volunteers differ
from nonvolunteers?
Volunteers are more sociable, score higher in social
desirability, hold more liberal social and political
attitudes, are less authoritarian and a score higher
on intellegence tests than non volunteers.
Context Variables
extraneous variables produces by experimental procedures created by the
research setting environment, like assignment of participats to conditions.
When might subjects select
the experiment?
When we allow subjects to sign up for
Why shouldn't you run your
friends in your experiment?
experiments whose titles differ in
Selecting your friends might bias your
their appeal:
sample, threatening external validity.
"The Memory Test Environment"
Both you and your friends might act
"The Heavy Metal Music" Experiment"
differently in your experiment than
However, this could be result in a
biased sample threatening external
validity.
strangers.
Summarize the folklore about
subjects
Subjects who sign up late in the semester may be less
motivated and may behave differently than those who
sign up earlier in the semester.
Rosenthal speculated that the differences seen at the
start and end of an experiment may be just as likely
due to changes in the experimenter.
Thank you for listening!