Laboratory Experiments
Benefits of the Lab
• As treated = intent to treat (usually)
• Confounding variables hopefully controlled
• DVs and IVs can be measured with greater
precision than in the field
• Experimenter can create different and unique
“worlds” to examine that may not appear in
nature
– Advantage for testing counterfactuals
– Some theories imply “dogs that don’t bark”
Today
• Classic psychological experiment in obedience
• Psychological experiment on stereotyping and
minority groups
• Game theory experiment using animals
• Voting experiments
Milgram Experiments
Stanley Milgram. 1963. Journal of
Abnormal and Social Psychology
Protocol
• 40 male subjects recruited from New Haven, CT
• Told they would participate in an experiment to
determine effect of punishment on learning
• Brought into waiting room, sat next to a
“confederate” of the experimenter.
• Drew slips of paper from a hat labeled “Teacher”
or “Learner”
– But both slips marked “Teacher” so subject was
always the Teacher
• Subjects always selected to be teacher, other
person in room (confederate), always student
• Subject taken to a room with a microphone,
panel of switches labeled “Slight Shock” to
“Danger: Severe Shock”
• Experimenter in room with subject to give
directions
• Experimenter tells subject to read list of word
pairs to “Student”
• Student asked to recall which word paired
with another
• If Student answers incorrectly, Teacher told by
experimenter to administer increasingly
severe electric shock
• Teacher hears reaction to (fake) shock through
speaker
If Teacher Refuses to Administer Shock
• Prod 1: Please continue. or Please go on.
• Prod 2: The experiment requires that you
continue.
• Prod 3: It is absolutely essential that you
continue.
• Prod 4: You have no other choice, you must go
on.
Measures
• DV is maximum shock subject administers
Maximum Shock Administered
• 5 subjects stopped at “Intense Shock”
• 9 stopped at “Extremely Intense Shock” to
“Danger Severe Shock”
• 26 did not stop until maximum shock
• Videos of subjects show intense concern
about well-being of “Student” and doubt
about the experiment
• But most subject continued
Importance
• Showed how far human obedience to
authority can extend
• Also showed dangers of social science
experiments and importance of human
subjects protection
Categorical and Contextual Bases of
Person Memory and Stereotyping
Shelley E. Taylor, Susan T. Fiske, Nancy L. Etcoff,
and Audrey J. Ruderman
Journal of Personality and Social Psychology
1978, Vol. 36, No. 7
Hypotheses
• People encode information by the race and
sex of the person they observe
• Minimize within-group differences and
exaggerate between-group differences
• Within-group attributes exaggerated in inverse
proportion to size of the minority group
Method
• 21 white Harvard students recruited to listen to an
audiotape of a group discussion
• Directions: “You are going to hear a tape of six men
discussing a publicity campaign for a play. To make it
easier for you to tell the six voices apart, we will also
show pictures of the men. As each person speaks, his
picture will be shown on the opposite wall. The
conversation lasts about 15 minutes. After the
conversation is over, you will be asked some questions
about the discussion. We are interested in several
different kinds of observations about the group.
Instead of having each of you answer all the same
questions, everyone will be given a separate task.”
Randomization
• Don't attend to anything in particular. While you watch, just
observe the interaction of the group as a whole and the
contributions of each of the participants. (Control
condition.)
• During the tape, each of the six participants makes a
number of specific suggestions about how to run the
publicity campaign. When the presentation is over, you will
be given a list of the suggestions and asked to match each
suggestion with a picture of the speaker. (Memory
condition.)
• The purpose of this memory versus control manipulation
was to see when categorization by race occurs
Protocol
• Subjects observed 15 minute audiotape
discussion with photos of 6 men, 3 black and 3
white
• Each participant made 6 suggestions during
discussion
• Photos shown of man talking randomized by
race
Protocol
• After hearing the carefully-scripted and balanced
discussion, subjects were told:
“You will now receive a separate page with pictures of
each of the six participants in the discussion you just
observed. Below each person's picture is a number. You
will also receive a list of all suggestions made on the
tape. In front of each suggestion there is a blank. Insert
the number of the picture of the person who made
that suggestion. In order for us to analyze the data, all
questions must be answered. Guess if you do not know
an answer.”
Dependent Variables
• Total number of errors
• Number of black suggestions incorrectly
attributed other blacks (BB)
• Number of white suggestions incorrectly
attributed to other whites (WW)
• Total number of intraracial errors (BB + WW)
• Number of white suggestions incorrectly
attributed to blacks (WB)
• Total interracial errors (BW + WB)
Results
Results
• People make more errors remembering
statements made by people of same race
• People encode information by the race of the
person they observe
Another Experiment
• Six persons, three males and three females, were
recruited to improvise a public school teacher's
lounge conversation.
• Six new persons, again three men and three
women, were next recruited to imitate each of
the original speakers; each original male speaker
was imitated by a female who mimicked him until
she was able to get the same intonations and
speech speed. The same was done with male
imitators of female original speakers.
Treatment
• Created taped conversations varying in sex
composition by splicing in imitators and
splicing out the appropriate original voices in
whatever combination was required.
Composition of Experiment Groups
Subjects
• 140 Harvard students
• Randomly assigned to hear and see slides of
one group conversation
• Subjects then rated group members on several
different traits
Results
• Perception of speaker varies by sex
composition of group
Experiments on Games, Markets,
Voting, and Committee Decisions
Boxed Pigs Game
• Two pigs are placed in a cage.
• A lever must be pressed so that food comes out
of a dispenser. There are no other source of food.
• Efforts must be spent to press the lever.
• Each pig has two strategies: either press the lever
or wait at the dispenser.
• Each pig’s utility is the amount of food consumed
less the efforts spent to press the lever
The boxed pigs game
Figure 3.14 The Boxed-Pigs Game
Harrington: Games, Strategies, and Decision Making, First Edition
Copyright © 2009 by Worth Publishers
Experimental results in the boxed pigs game:
Many Experiments Test Game Theory
• Students recruited to participate
• Paid small amounts of money for outcomes of
games
• Researcher structures payoffs to match the
underlying game theory model
• Can vary payoffs for several rounds for each
participant (within-subject) or across
participants (between-subject)
Should A Person Vote?
Standard Calculus of Voting Model
Vote if PB > C
P=probability of decisive vote
B=benefit from preferred candidate winning
C=cost of voting
Since C>0 and PB is very small, implies people
should not vote
Bayesian Models
• But, if no one should vote, then someone
should vote since he will be decisive
• Models incorporate beliefs about how many
other voters will vote
• Predictions
– Positive turnout
– Turnout increases with closeness of race
– More of “underdog’s” voters vote
Thomas R. Palfrey, “Laboratory Experiments in Political Economy”
Jury Games
• All jurors have common preferences:
– convict a guilty defendant, acquit the innocent
• Each juror has private “signal” about whether
defendant is guilty
• Jurors vote simultaneously or secretly
• Each juror believes each other juror’s
“informedness” (probability of receiving the
correct signal about defendant’s guilt) is
greater than .5
Equilibrium in Jury Game
• Solve for case in which a juror is pivotal: If he
is pivotal, most other jurors must believe
defendant is guilty
• One Equilibrium: No juror votes innocent
when in fact every juror believes the
defendant is innocent
Problems?
• The lab is an artificial environment
• Man is a social animal
• Context matters