300 W5 Discussion

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The Experiment

Chapter 7

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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

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

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

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

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

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.

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

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).

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.

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

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.

Do You Speak The Language Of Experimental Design?

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.

Experimental Validity Inside And Out

Threats to Internal Validity

Selection Bias

History

Maturation

Testing

Experimental Mortality

Contamination or Diffusion of Treatment

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.

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

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.

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

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

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

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

Making Comparisons And Looking At Experimental Results

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

History2. Artifical setting

3. Maturation3. Artifical treatment

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

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