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Business
Research Methods
William G. Zikmund
Chapter 12:
Experimental Research
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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
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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
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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.
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Experiment Treatment
Alternative manipulations of the
independent variable beinginvestigated
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Independent Variable
• The experimenter controls independent
variable.
• The variable’s value can be
manipulated by the experimenters to
whatever they wish it to be.
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Manipulation of Independent
Variable• Classificatory Vs. continuous variables
• Experimental and control groups
• Treatment levels
• More than one independent variable
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Experimental Treatments
• The alternative manipulations of the
independent variable being investigated
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Dependent Variable
• Its value is expected to be dependent
on the experimenter’s manipulation
• Criterion or standard by which the
results are judged
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Dependent Variable
• Selection
– e.g... sales volume, awareness, recall,
• Measurement
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Test Units
• Subjects or
entities whose
response to the
experimental
treatment are
measured or
observed.
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Two Types of Experimental
Error • Constant errors
• Random errors
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Field versus
Laboratory Experiments
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Controlling Extraneous Variables
• Elimination of extraneous variables
• Constancy of conditions
• Order of presentation
• Blinding
• Random assignment
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How May an Experimenter control for
Extraneous Variation?• Eliminate Extraneous Variables
• Hold Conditions Constant
• Randomization
• Matching Subjects
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Establishing Control
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Demand Characteristics
• Experimental procedures that intentionally
hint to subjects something about the
experimenter’s hypothesis
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Demand Characteristics
• Guinea pig effect
• Hawthorne effect
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Field Vs. Laboratory Experiment
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Laboratory Experiment Field Experiment
Artificial-Low Realism
Few ExtraneousVariables
High control
Low Cost
Short Duration
Subjects Aware of Participation
Natural-High Realism
Many ExtraneousVariables
Low control
High Cost
Long Duration
Subjects Unaware of Participation
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Control Groups
Isolate
extraneous
variation
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When does an Experiment have
Internal Validity?
Internal Validity - The ability of an
experiment to answer the question whether
the experimental treatment was the solecause of changes in a dependent variable
Did the manipulation do what it was supposed
to do?
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Factors Influencing Internal
Validity• History
• Maturation
• Testing
• Instrumentation
•Selection
• Mortality
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Isolating Extraneous Variation
with a Control Group• History Effects
• Maturation Effects
• Mortality Effects
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Type of Extraneous Variable Example
History - Specific events in theenvironment between the Beforeand After measurement that arebeyond the experimenter’s control
Maturation - Subjects changeduring the course of the experiment
Testing - The Before measure alerts
or sensitizes subject to nature of experiment or second measure.
A major employer closes its plant intest market area
Subjects becometired
Questionnaire
about the traditionalrole of womentriggers enhancedawareness of womenin an experiment.
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Instrument - Changes in
instrument result in response bias
Selection - Sample selection
error because of differentialselection comparison groups
Mortality - Sample attrition; somesubjects withdraw from experiment
New questions about
women are interpreteddifferently from earlier questions.
Control group and
experimental group isself-selected groupbased on preference for soft drinks
Subjects in one groupof a hair dying studymarry rich widows andmove to Florida
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How can Internal Validity
Increase?
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Increasing Internal Validity
• Control group
• Random assignment
• Pretesting and posttesting
• Posttest only
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What are the Different Basic
Experimental Designs?
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Quasi-Experimental Designs
• One Shot Design (After Only)
• One Group Pretest-Posttest
• Static Group Design
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One Shot Design (After Only)
X O1
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One Group Pretest-Posttest
O1 X O2
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Static Group Design
Experimental Group X O1
Control Group O2
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Three Good Experimental Designs
• Pretest - Posttest Control Group Design
• Posttest Only Control Group
• Solomon Four Group Design
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Pretest-Posttest Control Group Design
Experimental Group R O1 X O2
Control Group R O3 X O4
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Posttest Only Control Group
Experimental Group R X O1
Control Group R O2
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One-Shot Design
Internal Validity Problems
• History
– weak
• Maturation – weak
• Testing
– not relevant
• Instrumentation
– not relevant
• Selection – weak
• Mortality
– weak
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One-Group Pretest-Posttest
Internal Validity Problems
• History
– weak
• Maturation – weak
• Testing
– weak
• Instrumentation
– weak
• Selection – controlled
• Mortality
– controlled
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Static-Group Design
Internal Validity Problems
• History
– controlled
• Maturation – possible source of
concern
• Testing
– controlled
• Instrumentation
– controlled
• Selection – weak
• Mortality
– weak
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Pretest-Posttest Control
Internal Validity Problems• History
– controlled
• Maturation – controlled
• Testing
– controlled
• Instrumentation
– controlled
• Selection – controlled
• Mortality
– controlled
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Solomon Four-Group Design
Internal Validity Problems• History
– controlled
• Maturation – controlled
• Testing
– controlled
• Instrumentation
– controlled
• Selection – controlled
• Mortality
– controlled
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Posttest-Only Control
Internal Validity Problems• History
– controlled
• Maturation – controlled
• Testing
– controlled
• Instrumentation
– controlled
• Selection – controlled
• Mortality
– controlled
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Advanced Experimental Designs are
More Complex
• Completely randomized
• Randomized block design
• Latin square
• Factorial
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Completely Randomized Design
• An experimental design that uses a random
process to assign subjects (test units) and
treatments to investigate the effects of onlyone independent variable.
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Completely Randomized Designs
Average minutesshopper spendsin store
Control:no music
Experimentaltreatment:slow music
Experimentaltreatment:fast music
16 18 12
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Independent Variable A
Group A Group B Group C
Level 1 Level 2 Level 3
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Completely Randomized Design
With a pretest posttest
Group A R O1 X1 O2
Group A R O3 X2 O4
Group A R O5 X3 O6
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With a posttest
Group A R X1 O1
Group B R X2 O2
Group C R X3 O3
Completely Randomized Design
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Randomized Block Design
• An extension of the completely randomized
design in which a single extraneous variablethat might affect test units’ response to the
treatment has been identified and the effects
of this variable are isolated by blocking outits effects.