EXPERIMENTAL RESEARCH
BUSN 364 – Week 12
Özge Can

Stanford Marshmallow Experiment
 Measuring
delayed gratification (ability to wait in
order to obtain something you want)
 http://www.youtube.com/watch?v=x3S0xS2hdi4



A child is given a marshmallow and promised another,
only if they could wait before eating the first one.
Researchers measure how long the child resists the
temptation of eating it
Whether correlated with future success or not
Experimental Research

Builds on the principles of positivist perspective
and natural sciences
(1) Starts with a causal hypothesis
(2) Modify one specific aspect of a situation that is
closely connected to the cause, and
(3) Compare the outcome to what existed without the
modification
Example Experiment

Manipulation of Independent Variable
 Question: Do suggestions affect memories?
 Method: Randomly assign participants to groups
and tell some participants that dreams indicate
prior experience but do not tell that to other
participants.
 Results: Dream interpretations induce changes in
memories of past events.
 Conclusion: We can influence people’s memories
by giving them erroneous information
Attributes of Experiments




Can powerfully test causal relationships
An experiment is often artificial => includes
independent and dependent variables but exclude
confounding variables
Confounding Variables: Factors that are not part of
the intended hypothesis but have effects on variables of
interest
Best for issues that have a narrow scope and sharpened
focus
Attributes of Experiments



Isolates and targets one or a few causal variables; not
effective for considering dozens of variables
simultaneously
Best suited for micro-level (individuals, small-groups)
more than macro-level (entire society) theoretical
concerns
Practical and ethical limitations in social science
experiments => We cannot manipulate many
areas/conditions of human life
Power of Experimental Design

Is it better to study these with a survey or
experiment?
 Playing
violent video games increases aggressive
behavior
 Students who sit at the front of the classroom
make better grades than those that sit in the back
Power of Experimental Design

Consider recent changes that have been made
on your campus (e.g., changes in graduation
requirements or student life issues). Did the
administration use experiments or quasiexperiments to determine whether or not to
make these changes? Can you think of
situations in which an experimental approach
could have been used?
Parts of the Experiment
1.
2.
3.
4.
5.
6.
7.
Treatment or independent variable (IV)
Dependent variable (DV)
Pretest
Posttest
Experimental group
Control group
Random assignment
Parts of the Experiment



Treatment => (stimulus, manipulation) the independent
variable or a combination of independent variables in
experimental research
Dependent variable => the outcome in experimental
research. It is measured by paper-and-pencil tests,
observation, interviews or physiological responses (e.g.
heart beat, palm sweating)
Pretest => the measurement of the independent
variable prior to the introduction of the treatment.
Parts of the Experiment



Posttest => the measurement of the independent
variable after the treatment has been introduced into
the experiment situation
Experimental group => the group that receives the
treatment or in which treatment is present
Control group => the group that does not receive the
treatment
Random Assignment



Participants divided into groups at the beginning
of experimental research using a random process
so the experimenter can treat the groups as
equivalent
Randomness in statistical or mathematical sense: All
participants have an equal chance of ending up in one
or the other group
Increases our confidence that the groups do not differ
in any systematic way
Random Assignment
How to Randomly Assign?
Controls in Experiment




By controlling confounding effects and isolating the
effects of the treatment, we eliminate alternative
explanations
Deception: Sometimes we intentionally mislead participants
to control the experiment setting
 Deception involves using confederates and cover stories
(as false explanations)
Using placebo: simulated or ineffectual treatment intended
to deceive the participants
Blind studies: Single blind; double-blind
Steps in Experiment (1):
•
•
•
•
•
Hypothesis
Choose a design
Design experiment
– How to introduce IV
– How to measure DV
Locate subjects
Randomly assign subjects
Steps in Experiment (2):
•
•
•
Gather pretest data
Run experiment
– Introduce treatment
– Measure DV
– Gather posttest data
– Debrief
Analyze data
Types of Experimental Design

Classical Experimental Design:
 Includes
random assignment, a control group and
experimental group, and a pretest and posttest for each
group

Pre-Experimental Design:
 Lack
control group and random assignment
 Weaker than classical experiment
 Substitude classical experiments when they are not
possible
Types of Experimental Design

Quasi-Experimental Design
 We
call them “quasi” (apparently, as if) becuse they are
variations of the classical design
 Some have control group and randomization but lack a
pretest
Types of Experimental Design
Classical Experimental Design
Figure 8.6 Pretest-posttest control-group design.
Classical Experiment: Example



You have 40 newly hired waiters; you instruct them not to
introduce themselves with first name and not to return
during the meal to check on the customers
You randomly divide the waiters into two groups of 20
persons (random assignment) and send each group to
one of two restaurants to begin working.
You record the amount of tips for all participants for one
month (pretest score)
Classical Experiment: Example



Next, you retrain the group at restaurant A (experiment
group) and instruct them to introduce themselves with first
name and ask “Is everything fine?” 10 minutes after
delivering the food (treatment).
You remind the group at restaurant B (control group) to
continue as before.
Over the second month, you record the amount of tips for
both groups (posttest score)
Internal Validity



Occurs when the independent variable, and
nothing else, influences the dependent variable.
Anything other than independent variable threatens
internal validity
Artifacts => unwanted or confounding variables that
are due to the particular experimental arrangement
Threats to Internal Validity
 Selection

bias
A bias that arise when groups in an experiment are
not equivalent with regard to the DV
 History
 Something
occurs and affects the DV during an
experiment; is unplanned and outside the
researcher’s control
 Maturation
 Natural
processes of growth, boredom, fatigue that
occur during the experiment and affect DV
Threats to Internal Validity
 Testing:
The very process of measuring, the pretest
measure itself has an effect on DV
 Instrumentation:
Occurs when the instrument or
measure of the DV changes during the experiment
 Experimental
mortality
 Participant
fail to participate throughout the entire
experiment; they leave the experiment
 Demand
characteristics
 Participants
“guess” the study hypothesis and respond
to what they think the experimenter “demands” from
them
Threats to Internal Validity
 Diffusion
of treatment
 The
treatment “spills over” from the experimental
group and control group participants modify their
behavior because they learn of the treatment
 Compensatory
behavior
 When
participants in the control group modify their
behavior to make up for not getting the treatment
 Experimenter
 Experimenter
expectancy
indirectly makes participants aware of
the hypothesis or desired results
External Validity

The ability to generalize experiment findings

It addresses two major questions:
1. Can we generalize from the specific collection of
participants in one experiment to an entire population
=> Population generalization
2. Can we generalize from what occurs in a highly
controlled and artificial setting to most natural, “real
world” situations => Naturalistic generalization
External Validity
Field Experiments



An experiment that takes place in the “field”; a
natural setting instead of an artifical one
(laboratory)
They have lower internal validity but higher external
validity than laboratory experiments
Participants are usually unaware that they are involved
in an experiment and react in a natural way
 Example: A confederate fakes a heart attack on the
subway to see how the bystanders react
Field Experiments

Helping behavior and gender
 http://www.youtube.com/watch?v=BuyIOM4d-
OA&feature=related
Practical Considerations

Planning and pilot testing
 We
anticipate alternative explanations or threats to
internal validity during a good planning phase

Instructions to subjects
 Preparing
instructions carefully so that all participants
understand the exact same thing

Post-experiment interview
 Ethically
debriefing research participants the
deception; understanding what participants thought
and felt during the experiment
Online Resources:


This University of Denver site provides links to
various online experiments in which students can
participate.
http://www.du.edu/psychology/methods/
Watch it 


Super Size Me
Field experiment by Morgan Spurlock (2004)
 http://www.youtube.com/watch?v=4QezCOCVmg&feature=relmfu