Directions
- Post your full answer to the question by 11:59 p.m., Thursday, CT.
- Respond to 2 different students with one or more of the following by 11:59 p.m., Sunday, CT:
A link that brings in new information or helps the student you’re responding to
A substantial question (not, “what do you think?”)
A politely worded critique that shows either a flaw in your classmate’s logic, misunderstanding of the data, or a failure to fully answer the questions
For this discussion section find two new peer-reviewed academic journal articles that directly relate to your research topic for this class and
rely on experimental designs
.
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1. Describe both experiments and the findings with reference to:
· Type of experimental design (Between, Within, or Mixed);
· How participants were assigned to conditions?
· How did they manage threats to external and internal validity (if at all)?
2. Then describe how the studies you discussed in this discussion section may help you develop your own research project either methodologically or in terms of your question/hypothesis.
In summary, for this assignment, you are going to: 1) Find, 2) Describe, and 3) Apply.
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The Experiment
Chapter 7
Copyright © Allyn & Bacon 2009
Doing Experiments In Everyday Life
Experiments in psychology use the same logic that guides experiments in biology or engineering.
Experimental research is strongest for testing causal relationships.
Experiments most clearly satisfy the three conditions needed to demonstrate causality—temporal order, association, and no alternative explanations.
Copyright © Allyn & Bacon 2009
Doing Experiments In Everyday Life
You can do two types of comparisons:
Before-and-after comparison
Side-by-side comparison
You do three things in an experiment:
Start with a cause-effect hypothesis,
Modify a situation or introduce a change,
Compare outcomes with and without the modification.
Copyright © Allyn & Bacon 2009
What Questions Can You Answer With the Experimental Method?
Research questions most appropriate for an experiment fit its strengths and limitations. These include:
a clear and simple logic,
the ability to isolate a causal mechanism,
targeted on two or three variables and narrow in scope,
limited by practical and ethical aspects of the situations you can impose on humans.
Copyright © Allyn & Bacon 2009
Why Assign People Randomly?
The purpose of random assignment is to create equivalent groups.
Random Assignment = Sort research participants into two or more groups in a mathematically random process.
Matching versus Random Assignment
True matching on more than one or two characteristics is nearly impossible.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
A true experiment includes:
Independent variable
Dependent variable
Pretest
Pretest = A measure of the dependent variable prior to introducing the independent variable in an experiment.
Posttest
Posttest = A measure of the dependent variable after the independent variable has been introduced in an experiment.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
A true experiment includes (cont):
Experimental group
Experimental group = In an experiment with multiple groups, a group of participants that receives the independent variable or a high level of it.
Control group
Control Group = In an experiment with multiple groups, a group of participants that does not receive the independent variable or a very low level of it.
Random assignment
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Types of Experimental Design
Independent group design = Experimental designs in which you use two or more groups and each gets a different level of the independent variable.
Repeated Measures Design = An experimental design with a single participant group but that receives different levels of the independent variable.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Steps in Conducting an Experiment
Begin with a straightforward hypothesis appropriate for experimental research.
Decide on an experimental design to test the hypothesis within practical limitations.
Decide how to introduce the independent variable.
Develop a valid and reliable measure of the dependent variable.
Set up an experimental setting and conduct a pilot test of the variables.
Locate appropriate participants.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Steps in Conducting an Experiment (cont.)
Randomly assign participants to groups and give careful instructions.
Gather data for the pretest measure of the dependent variable.
Introduce the independent variable to the experimental group only and monitor all groups.
Gather data for posttest measure of the dependent variable.
Debrief the participants.
Examine data collected and make comparisons between different groups using statistics to determine whether the data support the hypothesis.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Managing Experiments
Isolation of effects of independent variable
Elimination of alternative explanations
Confederates = people who work for an experimenter and mislead participants by pretending to be another participant or an uninvolved bystander.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Types of Experimental Design
Experimental design = How parts of an experiment are arranged, often in one of the standard configurations.
True Experimental Designs
Classical experimental design = An experimental design that has all key elements that strengthen its internal validity: random assignment, control and experimental groups, and pretest and protest
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Example: Classical Experimental Design
Sheet1
Month 1 Month 2
Randomly Assign Participants to training sessions Group 1 Pretest Independent Variable Present Posttest
Serve food without introduction or checking (amount of tips) Self introduction and return to check on customer (amount of tips)
Group 2 Pretest Independent Variable Absent Posttest
Serve food without introduction or checking (amount of tips) Serve food without introduction or checking (amount of tips)
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Example: Two-Group Posttest Only Experimental Design
Sheet1
Month 1 Month 2
Randomly Assign Participants to training sessions Group 1 Pretest Independent Variable Present Posttest
Serve food without introduction or checking (amount of tips) Self introduction and return to check on customer (amount of tips)
Group 2 Pretest Independent Variable Absent Posttest
Serve food without introduction or checking (amount of tips) Serve food without introduction or checking (amount of tips)
Month 1 Month 2
Randomly Assign Participants to training sessions Group 1 Independent Variable Present Posttest
Serve food without introduction or checking RETRAIN Self introduction and return to check on customer (amount of tips)
Group 2 Independent Variable Absent Posttest
Serve food without introduction or checking Continue to Serve food without introduction or checking (amount of tips)
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Example: Solomon 4-Group Experimental Design
Sheet1
Month 1 Month 2
Randomly Assign Participants to training sessions Group 1 Independent Variable Present RETRAIN Self introduction and return to check on customer Posttest
Serve food without introduction or checking (amount of tips)
Group 2 Independent Variable Absent Posttest
Serve food without introduction or checking Continue to Serve food without introduction or checking (amount of tips)
Month 1 Month 2
Randomly Assign Participants to training sessions Group 1 Pretest Independent Variable Present Posttest
Serve food without introduction or checking (amount of tips) RETRAIN Self introduction and return to check on customer (amount of tips)
Group 2 Pretest Independent Variable Absent Posttest
Serve food without introduction or checking (amount of tips) Continue to serve food without introduction or checking (amount of tips)
Group 3 Independent Variable Present Posttest
Serve food without introduction or checking RETRAIN Self introduction and return to check on customer) (amount of tips)
Group 4 Independent Variable Absent Posttest
Serve food without introduction and checking Continue to serve food without introduction or checking (amount of tips)
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Example: Latin Square Experimental Design
Sheet1
Customer Arrives 10 minutes After Food After Customer Finishes Meal Posttest
Randomly Assign Participants to training sessions Group 1 Check on Customer Offer dessert or bill Amount of tips
Group 2 Take order Check on Customer Amount of tips
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Types of Experimental Design
True Experimental Designs
Factorial Design = An experimental design in which you examine the impact of combinations of two or more independent variable conditions.
Main Effects = The effect of a single independent variable on a dependent variable.
Interaction Effects = The effect of two or more independent variables in combination on a dependent variable that is beyond or different from the effect that each has alone.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Example: Factorial Experimental Design
Sheet1
Month 1 Month 2
Randomly Assign Participants to training sessions All Female Group 1 Pretest Independent Variable Present Posttest
Serve food without introduction or checking (amount of tips) RETRAIN Self introduction and return to check on customer (amount of tips)
All Female Group 2 Pretest Independent Variable Absent Posttest
Serve food without introduction or checking (amount of tips) Serve food without introduction or checking (amount of tips)
All Male Group 3 Pretest Independent Variable Present Posttest
Serve food without introduction or checking (amount of tips) RETRAIN Self introduction and return to check on customer (amount of tips)
All Male Group 4 Pretest Independent Variable Absent Posttest
Serve food without introduction and checking (amount of tips) Serve food without introduction or checking (amount of tips)
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Preexperimental designs = Experimental designs that lack one or more parts of the classical experimental design.
One-Shot Case Study Design. (one-group posttest-only design)
One-Group Pretest-Posttest Design.
Static Group Comparison. (posttest-only nonequivalent group design).
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Quasi-experimental Designs = Experimental Designs that approximate the strengths of the classical experimental design but do not contain all its parts.
Interrupted Time Series.
Equivalent Time Series.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Sheet1
A Comparison of Experimental Designs
Random Control Experimental
Design Assignment Pretest Posttest Group Group
PREEXPERIMENTAL
One-Shot Case Study No No Yes No Yes
One-Group Pretest Postest No Yes Yes No Yes
Static Group Comparison No No Yes Yes Yes
TRUE EXPERIMENTAL
Classical Yes Yes Yes Yes Yes
Two-Group Posttest Only No Yes Yes Yes Yes
Solomon Four Group Yes Yes Yes Yes Yes
Latin Square Yes Yes Yes Yes Yes
Factoral Yes Yes Yes Yes Yes
QUASI-EXPERIMENTAL
Two-Group Posttest Only Yes No Yes Yes Yes
Time Series Designs No Yes Yes No Yes
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Design notation = A symbol system to express the parts of an experimental design with X, O and R.
O = observation of dependent variable
X = independent variable
R = random assignment.
Copyright © Allyn & Bacon 2009
Do You Speak The Language Of Experimental Design?
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
Looking at an Experiment’s Internal Validity
Internal Validity = The ability to state that the independent variable was the one sure cause that produced a change in the dependent variable.
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
Threats to Internal Validity
Selection Bias
History
Maturation
Testing
Experimental Mortality
Contamination or Diffusion of Treatment
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
Threats to Internal Validity
Experimenter Expectancy
Double blind experiment = An experimental design to control experimenter expectancy in which the researcher does not have direct contact with participants. All contact is through assistants from whom some details are withheld.
Placebo = A false or non-effective independent variable given to mislead participants.
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
External Validity and Field Experiments
External validity = An ability to generalize experimental findings to events and settings beyond the experimental setting itself.
Threats to external validity:
Participants are not representative
Artificial setting
Artificial treatment
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
External Validity and Field Experiments
Threats to external validity (cont)
Reactivity = participants modifying their behavior because they are aware that they are in a study.
Hawthorne effect = a type of experimental reactivity in which participants change due to their awareness of being in a study and the attention they receive from researchers.
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
External Validity and Field Experiments
Field experiment = An experiment that takes place in a natural setting and over which experimenters have limited control.
Less internal validity
More external validity
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
Sheet1
Seven Threats to INTERNAL VALIDITY Four Threats to EXTERNAL VALIDITY
1. Selection 1. Participants not representative
2. History 2. Artifical setting
3. Maturation 3. Artifical treatment
4. Testing 4. Reactivity
5. Experimental Morality
6. Contamination
7. Experimenter Expectancy
Sheet2
Sheet3
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
Natural experiments = Events that were not initially planned to be experiments but permitted measures and comparisons that allowed the use of an experimental logic.
Also called ex post facto—after the fact
Copyright © Allyn & Bacon 2009
Experimental Validity Inside And Out
Practical techniques to carry out effective experiments
Planning and Pilot Tests
Instructions to Participants
Post-experiment Interview
Debrief = An interview or talk with participants after an experiment ends in which you remove deception if used and try to learn how they understood the experimental situation
Copyright © Allyn & Bacon 2009
Making Comparisons And Looking At Experimental Results
Copyright © Allyn & Bacon 2009
How To Be Ethical In Experiments
Experimenters must carefully consult with IRBs.
Deception is acceptable BUT dishonesty is NOT!
Debriefing is a MUST.
Group 1Pretest
Independent
Variable
Present
Posttest
Serve food
without
introduction
or checking
(amount of tips)
Self
introduction
and return to
check on
customer
(amount of tips)
Group 2 Pretest
Independent
Variable
Absent
Posttest
Serve food
without
introduction
or checking
(amount of tips)
Serve food
without
introduction
or checking
(amount of tips)
Month 1Month 2
Randomly
Assign
Participants to
training
sessions
Group 1
Independent Variable
Present
Posttest
Serve food without
introduction or
checking
RETRAIN Self
introduction and
return to check on
customer
(amount of tips)
Group 2
Independent Variable
Absent
Posttest
Serve food without
introduction or
checking
Continue to Serve
food without
introduction or
checking
(amount of tips)
Randomly
Assign
Participants to
training
sessions
Month 1Month 2
Seven Threats to INTERNAL
VALIDITY
Four Threats to EXTERNAL
VALIDITY
1. Selection
1. Participants not
representative
2.
History2. Artifical setting
3. Maturation3. Artifical treatment
4.
Testing4.
Reactivity
5. Experimental Morality
6. Contamination
7. Experimenter Expectancy
A Comparison of Experimental Designs
RandomControlExperimental
DesignAssignmentPretestPosttestGroupGroup
PREEXPERIMENTAL
One-Shot Case StudyNoNoYesNoYes
One-Group Pretest PostestNoYesYesNoYes
Static Group ComparisonNoNoYesYesYes
TRUE EXPERIMENTAL
ClassicalYesYesYesYesYes
Two-Group Posttest OnlyNoYesYesYesYes
Solomon Four GroupYesYesYesYesYes
Latin SquareYesYesYesYesYes
FactoralYesYesYesYesYes
QUASI-EXPERIMENTAL
Two-Group Posttest OnlyYesNoYesYesYes
Time Series DesignsNoYesYesNoYes
Group
1
Group
2
Take order
Customer
Arrives
Randomly
Assign
Participants to
training
sessions
Self
introduction
and take order
Check on
Customer
Offer dessert or
bill
Check on
Customer
Self
introduction
and offer
dessert or bill
Posttest
Amount of
tips
Amount of
tips
10 minutes After
Food
After Customer
Finishes Meal
Group 1Pretest
Independent Variable
Present
Posttest
Serve food without
introduction or checking
(amount of
tips)
RETRAIN Self
introduction and return
to check on customer
(amount of
tips)
Group 2 Pretest
Independent Variable
Absent
Posttest
Serve food without
introduction or checking
(amount of
tips)
Continue to serve food
without introduction or
checking
(amount of
tips)
Group 3
Independent Variable
Present
Posttest
Serve food without
introduction or checking
RETRAIN Self
introduction and return
to check on customer)
(amount of
tips)
Group 4
Independent Variable
Absent
Posttest
Serve food without
introduction and
checking
Continue to serve food
without introduction or
checking
(amount of
tips)
Month 2
Randomly
Assign
Participants to
training sessions
Month 1
All Female Group 1 Pretest
Independent Variable
Present
Posttest
Serve food without
introduction or
checking
(amount of
tips)
RETRAIN Self
introduction and
return to check on
customer
(amount of
tips)
All Female Group 2 Pretest
Independent Variable
Absent
Posttest
Serve food without
introduction or
checking
(amount of
tips)
Serve food without
introduction or
checking
(amount of
tips)
All Male Group 3 Pretest
Independent Variable
Present
Posttest
Serve food without
introduction or
checking
(amount of
tips)
RETRAIN Self
introduction and
return to check on
customer
(amount of
tips)
All Male Group 4 Pretest
Independent Variable
Absent
Posttest
Serve food without
introduction and
checking
(amount of
tips)
Serve food without
introduction or
checking
(amount of
tips)
Month 1
Randomly
Assign
Participants to
training
sessions
Month 2
