Essentials of
Marketing Research
William G. Zikmund
Chapter 9: Experimental Research
Experiment
• A research investigation in which conditions are
controlled
• One independent variable is manipulated
(sometimes more than one)
• Its effect on a dependent variable is measured
• To test a hypothesis
Basic Issues of Experimental
Design
• Manipulation of the Independent Variable
• Selection of Dependent Variable
• Assignment of Subjects (or other Test
Units)
• Control Over Extraneous Variables
The experimenter has some degree of
control over the independent variable.
The variable is independent because its
value can be manipulated by the
experimenter to whatever he or she
wishes it to be.
Experiment Treatment
Alternative manipulations of the
independent variable being
investigated
Independent Variable
• The experimenter controls independent
variable.
• The variable’s value can be
manipulated by the experimenters to
whatever they wish it to be.
Manipulation of Independent
Variable
•
•
•
•
Classificatory vs. continuous variables
Experimental and control groups
Treatment levels
More than one independent variable
Experimental Treatments
• The alternative manipulations of the
independent variable being investigated
Dependent Variable
• Its value is expected to be dependent
on the experimenter’s manipulation
• Criterion or standard by which the
results are judged
Dependent Variable
• Selection
– e.g... sales volume, awareness, recall,
• Measurement
Test Units
• Subjects or
entities whose
response to the
experimental
treatment are
measured or
observed.
Two Types of Experimental Error
• Constant errors
• Random errors
Field versus
Laboratory Experiments
Controlling Extraneous Variables
•
•
•
•
•
Elimination of extraneous variables
Constancy of conditions
Order of presentation
Blinding
Random assignment
How May an Experimenter control for
Extraneous Variation?
•
•
•
•
Eliminate Extraneous Variables
Hold Conditions Constant
Randomization
Matching Subjects
Establishing Control
Demand Characteristics
• Experimental procedures that intentionally
hint to subjects something about the
experimenter’s hypothesis
Demand Characteristics
• Guinea pig effect
• Hawthorne effect
Field vs. Laboratory Experiment
Laboratory Experiment
Field Experiment
Artificial-Low Realism
Natural-High Realism
Few Extraneous
Variables
Many Extraneous
Variables
High control
Low control
Low Cost
High Cost
Short Duration
Long Duration
Subjects Aware of
Participation
Subjects Unaware of
Participation
Control Groups
Isolate
extraneous
variation
When does an Experiment have
Internal Validity?
Internal Validity - The ability of an
experiment to answer the question whether
the experimental treatment was the sole
cause of changes in a dependent variable
Did the manipulation do what it was supposed
to do?
Factors Influencing Internal
Validity
•
•
•
•
•
•
History
Maturation
Testing
Instrumentation
Selection
Mortality
Isolating Extraneous Variation
with a Control Group
• History Effects
• Maturation Effects
• Mortality Effects
Type of Extraneous Variable
Example
History - Specific events in the
environment between the Before
and After measurement that are
beyond the experimenter’s control
A major employer
closes its plant in
test market area
Maturation - Subjects change
during the course of the experiment
Subjects become
tired
Testing - The Before measure alerts
or sensitizes subject to nature of
experiment or second measure.
Questionnaire
about the traditional
role of women
triggers enhanced
awareness of women
in an experiment.
Instrument - Changes in
instrument result in response bias
New questions about
women are interpreted
differently from earlier
questions.
Selection - Sample selection
error because of differential
selection comparison groups
Control group and
experimental group is
self-selected group
based on preference for
soft drinks
Mortality - Sample attrition; some
subjects withdraw from experiment
Subjects in one group
of a hair dying study
marry rich widows and
move to Florida
How can Internal Validity
Increase?
Increasing Internal Validity
• Control group
• Random assignment
• Pretesting and posttesting
• Posttest only
What are the Different Basic
Experimental Designs?
Quasi-Experimental Designs
• One Shot Design (After Only)
• One Group Pretest-Posttest
• Static Group Design
One Shot Design (After Only)
X
O1
One Group Pretest-Posttest
O1
X
O2
Static Group Design
Experimental Group
Control Group
X
O1
O2
Three Good Experimental Designs
• Pretest - Posttest Control Group Design
• Posttest Only Control Group
• Solomon Four Group Design
Pretest-Posttest Control Group Design
Experimental Group
R O1 X O2
Control Group
R O3 X O4
Posttest Only Control Group
Experimental Group
R
Control Group
R
X
O1
O2
One-Shot Design
Internal Validity Problems
• History
– weak
• Instrumentation
– not relevant
• Maturation
• Selection
– weak
– weak
• Testing
– not relevant
• Mortality
– weak
One-Group Pretest-Posttest
Internal Validity Problems
• History
• Instrumentation
– weak
– weak
• Maturation
• Selection
– weak
• Testing
– weak
– controlled
• Mortality
– controlled
Static-Group Design
Internal Validity Problems
• History
– controlled
• Maturation
– possible source of
concern
• Testing
– controlled
• Instrumentation
– controlled
• Selection
– weak
• Mortality
– weak
Pretest-Posttest Control
Internal Validity Problems
• History
– controlled
• Maturation
– controlled
• Testing
– controlled
• Instrumentation
– controlled
• Selection
– controlled
• Mortality
– controlled
Solomon Four-Group Design
Internal Validity Problems
• History
– controlled
• Maturation
– controlled
• Testing
– controlled
• Instrumentation
– controlled
• Selection
– controlled
• Mortality
– controlled
Posttest-Only Control
Internal Validity Problems
• History
– controlled
• Maturation
– controlled
• Testing
– controlled
• Instrumentation
– controlled
• Selection
– controlled
• Mortality
– controlled
Solomon Four Group Design
Experimental Group 1:
Control Group 1:
Experimental Group 2:
Control Group 2:
R O1 X
R O3
R
X
R
X
O2
O4
O5
O6
Test Marketing
• Test marketing is an experimental procedure
that provides an opportunity to test a new
product or a new marketing plan under
realistic market conditions to measure sales
or profit potential.
Selecting A Test Market
•
•
•
•
•
•
•
Population size
Demographic composition
Lifestyle considerations
Competitive situation
Media
Self-contained trading area
Secrecy
Control Method
Of Test Marketing
• Small city
• Low chance of being detected
• Distribution is forced (guaranteed)
Advanced Experimental Designs
Are More Complex
•
•
•
•
Completely randomized
Randomized block design
Latin square
Factorial
Complex Experimental Designs
Control:
no music
Average minutes
shopper spends
in store
16
Experimental
treatment:
slow music
18
Experimental
treatment:
fast music
12
RANDOMIZED BLOCK DESIGN
Independent Variable
Control:
Experimental Experimental
no music treatment:
treatment:
slow music
fast music
Morning and
afternoons
Evening
hours
Factorial Design
Independent Variable 1
No Music
No grocery
cart signs
Grocery cart
signs
Slow Music
Fast Music
2 x 2 Factorial Design
Ad A
Ad B
Men
65
Effects
> Main
of Gender
Women
65
70
60
Main Effects of Ad
Interaction Between Gender and Advertising Copy
100
90
80
70
60
50
40
30
20
10
Ad A
Ad B
Factorial Design -- Roller Skates
Package Design
Price
Red
Gold
$25
$30
$35
Cell 1
Cell 2
Cell 3
Cell 4
Cell 5
Cell 6